# List of professional services firms in Ohio

Tamtam tracks 195 professional services firms headquartered in Ohio. This list ranks the 50 largest by number of employees on LinkedIn, led by Staffmark, CBIZ and Medpace. Their median headcount is 1,045. Half of them were founded in 1977 or later. The most common headquarters are Cincinnati (12), Columbus (8) and Cleveland (7).

This list of professional services firms in Ohio includes a mix of large established companies and mid-sized firms. The services offered range from staffing and IT consulting to legal and business consulting. Key players include Staffmark, a staffing company, CBIZ, which provides financial and employee business services, and Medpace, a global contract research organization for drug development.

A notable pattern is the concentration of headquarters in Cincinnati, which hosts Staffmark, Medpace, Belcan, Taft Stettinius & Hollister, RDI Corporation, and Dinsmore & Shohl. Other significant hubs are Cleveland and Columbus. The companies represent diverse sectors such as law practice, IT services, and specialized research.

🇺🇸 Ohio · 50 companies · Updated Nov 11, 2026

| # | Company | Industry | Headquarters | Employees | Founded |
|---|---|---|---|---|---|
| 1 | [Staffmark](https://www.tamtam.ai/c/staffmark) (staffmark.com)<br>Staffing company focused on matching jobs with exceptional people, delivering top customer satisfaction with industry-leading service quality Join us today! | Staffing and Recruiting | 🇺🇸 Cincinnati | 8,923 |  |
| 2 | [CBIZ](https://www.tamtam.ai/c/cbiz) (cbiz.com)<br>A national firm providing financial and employee business services, including accounting, employee benefits, risk consulting, valuation, and investment services | Business Consulting and Services | 🇺🇸 Independence | 8,651 | 1996 |
| 3 | [Medpace](https://www.tamtam.ai/c/medpace) (medpace.com)<br>Global CRO accelerating drug, biologic, and medical device clinical development through high-science expertise in various therapeutic areas worldwide | Pharmaceutical Manufacturing | 🇺🇸 Cincinnati | 6,421 | 1992 |
| 4 | [AML RightSource](https://www.tamtam.ai/c/aml-rightsource) (amlrightsource.com)<br>Provides trained professionals for Anti-Money Laundering, Bank Secrecy Act, and financial crimes compliance, including transaction monitoring and due diligence. | Financial Services | 🇺🇸 Cleveland | 6,341 |  |
| 5 | [Battelle](https://www.tamtam.ai/c/battelle) (battelle.org)<br>A science and technology company solving critical issues through research, development, manufacturing, and services for government and commercial clients worldwide | Research Services | 🇺🇸 Columbus | 6,013 | 1929 |
| 6 | [Belcan](https://www.tamtam.ai/c/belcan) (belcan.com)<br>Global provider of engineering, manufacturing, workforce, and IT solutions for aerospace, defense, automotive, industrial, and private sector clients for over 60 years | IT Services and IT Consulting | 🇺🇸 Cincinnati | 5,115 |  |
| 7 | [Squire Patton Boggs](https://www.tamtam.ai/c/squire-patton-boggs) (squirepattonboggs.com)<br>A global law firm with over 1,500 lawyers across four continents, providing legal insight and support for businesses in various sectors | Law Practice | 🇺🇸 Cleveland | 3,630 | 1886 |
| 8 | [ICC](https://www.tamtam.ai/c/icc-columbus) (g2o.com)<br>ICC provides user-centric, data-driven technology solutions through Business Intelligence, Application Integration & Development, and User Experience services for various industries | IT Services and IT Consulting | 🇺🇸 Columbus | 2,949 | 1978 |
| 9 | [Taft Stettinius & Hollister LLP](https://www.tamtam.ai/c/taft-stettinius-and-hollister-llp) (taftlaw.com)<br>A client-focused legal and government affairs consulting firm offering innovative solutions and advocacy at federal, state, and local levels | Law Practice | 🇺🇸 Cincinnati | 2,217 | 1885 |
| 10 | [RDI Corporation](https://www.tamtam.ai/c/rdi-corporation) (rdicorp.com)<br>A comprehensive business solutions provider offering customized outsourced services including contact center, IT, market research, and digital strategy support | Outsourcing and Offshoring Consulting | 🇺🇸 Cincinnati | 1,947 | 1978 |
| 11 | [Woolpert](https://www.tamtam.ai/c/woolpert) (woolpert.com)<br>A global architecture, engineering, geospatial, and strategic consulting firm serving public, private, and government clients worldwide with a focus on innovation and growth | Professional Services | 🇺🇸 Dayton | 1,843 | 1911 |
| 12 | [RoviSys](https://www.tamtam.ai/c/rovisys) (rovisys.com)<br>An independent control system integrator offering comprehensive process automation solutions and services with a focus on open systems and client choices | Automation Machinery Manufacturing | 🇺🇸 Aurora | 1,841 | 1989 |
| 13 | [Nesco Resource](https://www.tamtam.ai/c/nesco-resource) (nescoresource.com)<br>Connecting companies with talent, candidates with opportunities through flexible staffing solutions including contract, contract-to-hire, and direct placement services. | Staffing and Recruiting | 🇺🇸 Mayfield Heights | 1,759 | 1956 |
| 14 | [Dinsmore & Shohl LLP](https://www.tamtam.ai/c/dinsmore-and-shohl-llp) (dinsmore.com)<br>A nationwide team of over 750 attorneys providing high-quality, cost-effective legal advice to leading businesses, institutions, and individuals, with a focus on client service and workplace culture | Law Practice | 🇺🇸 Cincinnati | 1,719 | 1908 |
| 15 | [NAMSA](https://www.tamtam.ai/c/namsa) (namsa.com)<br>A leading MedTech Contract Research Organization specializes in helping medical device sponsors accelerate product development globally with proven solutions | Business Consulting and Services | 🇺🇸 Toledo | 1,659 | 1967 |
| 16 | [SSOE Group](https://www.tamtam.ai/c/ssoe-group) (ssoe.com)<br>Internationally recognized architecture and engineering firm specializing in providing high-quality project solutions for various industries with global reach | Engineering Services | 🇺🇸 Toledo | 1,634 | 1948 |
| 17 | [Davey Resource Group, Inc.](https://www.tamtam.ai/c/davey-resource-group-inc) (davey.com)<br>The company provides innovative solutions and expertise to a diverse range of clients in industries such as utilities, transportation, telecommunications, and government | Business Consulting and Services | 🇺🇸 Kent | 1,605 | 1992 |
| 18 | [FBT Gibbons](https://www.tamtam.ai/c/fbt-gibbons) (fbtgibbons.com)<br>A nationwide law firm with over 575 attorneys providing expert legal advice and representation in a variety of industries across the United States | Law Practice | 🇺🇸 Cincinnati | 1,536 | 1919 |
| 19 | [The Planet Group](https://www.tamtam.ai/c/the-planet-group) (theplanetgroup.com)<br>A diversified organization providing human capital solutions and consulting services to Fortune 500 clients in technology, energy, finance, HR, administrative, and marketing industries | Staffing and Recruiting | 🇺🇸 Westlake | 1,417 | 2009 |
| 20 | [Hylant](https://www.tamtam.ai/c/hylant) (hylant.com)<br>A leading full-service insurance brokerage with nationwide presence, offering risk management, employee benefits, wellness strategies, insurance solutions for businesses and individuals | Insurance | 🇺🇸 Toledo | 1,329 | 1935 |
| 21 | [Part Time Works](https://www.tamtam.ai/c/part-time-works) (PartTimeWorks.com)<br>Specializing in part-time professional placement services, we connect job seekers with organizations seeking efficient, effective part-time staffing solutions for long-term employment | Staffing and Recruiting | 🇺🇸 Columbus | 1,169 | 2012 |
| 22 | [Centric Consulting](https://www.tamtam.ai/c/centric-consulting) (centricconsulting.com)<br>Provides AI strategy, cyber risk management, cloud solutions, and tailored consulting services with experienced advisors and scalable teams. | Business Consulting and Services | 🇺🇸 Dayton | 1,159 | 1999 |
| 23 | [Advantage Resourcing](https://www.tamtam.ai/c/advantage-resourcing) (advantageresourcing.com)<br>An experienced recruitment company offering talent placement in various industries and stages of career, with global reach and comprehensive services | Staffing and Recruiting | 🇺🇸 Cincinnati | 1,087 |  |
| 24 | [CBIZ Advisory Services](https://www.tamtam.ai/c/cbiz-advisory-services) (cbiz.com)<br>A financial services division providing accounting, tax, consulting, audit, and industry-specific services to clients nationwide, in collaboration with an independent CPA firm | Accounting | 🇺🇸 Cleveland | 1,055 |  |
| 25 | [Cohen & Co](https://www.tamtam.ai/c/cohen-and-co) (cohenco.com)<br>A highly reputable tax and accounting firm offering assurance, tax, and advisory services to a wide range of clients globally Founded in 1977 with over 800 professionals | Accounting | 🇺🇸 Cleveland | 1,045 | 1977 |
| 26 | [E Tech Group](https://www.tamtam.ai/c/e-tech-group) (etechgroup.com)<br>A leading engineering and system integration firm providing automation solutions to various industries with a team of over 450 engineers | Automation Machinery Manufacturing | 🇺🇸 West Chester | 1,010 | 1993 |
| 27 | [Advantage Technical](https://www.tamtam.ai/c/advantage-technical) (advantagetechnical.com)<br>This company specializes in aligning individuals with job opportunities that match their experience, skills, motivation, and goals | Staffing and Recruiting | 🇺🇸 Cincinnati | 986 |  |
| 28 | [Health Carousel](https://www.tamtam.ai/c/health-carousel) (healthcarousel.com)<br>A total talent management company providing healthcare staffing solutions to ensure US patients have access to qualified professionals when needed | Hospitals and Health Care | 🇺🇸 Cincinnati | 984 | 2004 |
| 29 | [Benesch Law](https://www.tamtam.ai/c/benesch-law) (beneschlaw.com)<br>Provides sophisticated legal services to national and international public and private companies, private equity funds, entrepreneurs, and not-for-profit organizations. | Law Practice | 🇺🇸 Cleveland | 949 | 1938 |
| 30 | [Thompson Hine LLP](https://www.tamtam.ai/c/thompson-hine-llp) (thompsonhine.com)<br>A leading full-service business law firm known for innovation, offering efficient, client-focused legal services through Thompson Hine SmartPaTH® | Law Practice | 🇺🇸 Cleveland | 933 | 1911 |
| 31 | [DLZ Corporation](https://www.tamtam.ai/c/dlz-corporation) (dlz.com)<br>A top consulting firm in architecture/engineering, DLZ works on projects nationwide, focusing on client service, innovation, and turning visions into reality | Architecture and Planning | 🇺🇸 Columbus | 911 | 1946 |
| 32 | [GPRS](https://www.tamtam.ai/c/gprs) (gp-radar.com)<br>The company specializes in damage prevention, data collection, existing condition documentation, and facility & project management using innovative technology and software solutions | Construction | 🇺🇸 Maumee | 894 | 2001 |
| 33 | [Lisinski Law Firm](https://www.tamtam.ai/c/lisinski-law-firm) (lisinskifirm.com)<br>Dedicated attorneys provide nationwide legal representation for immigration cases, advocating for client rights and compassionate support to remain with family | Legal Services | 🇺🇸 Dublin | 880 | 2020 |
| 34 | [The Reserves Network](https://www.tamtam.ai/c/the-reserves-network) (trnstaffing.com)<br>Provides personalized staffing services across multiple industries, placing temporary, temporary-to-hire, and direct-hire employees nationwide. | Staffing and Recruiting | 🇺🇸 Fairview Park | 876 | 1984 |
| 35 | [Crown Staffing](https://www.tamtam.ai/c/crown-staffing) (crownstaffing.com)<br>A staffing company providing innovative personnel solutions to companies and individuals in the Midwest and southern United States since 1968 | Staffing and Recruiting | 🇺🇸 Westerville | 873 | 1968 |
| 36 | [Vorys, Sater, Seymour and Pease LLP](https://www.tamtam.ai/c/vorys-sater-seymour-and-pease-llp) (vorys.com)<br>A pioneering firm providing innovative solutions for clients for over 100 years, with a team of 375 attorneys across 10 offices worldwide | Law Practice | 🇺🇸 Columbus | 869 | 1909 |
| 37 | [Burgess & Niple](https://www.tamtam.ai/c/burgess-and-niple) (burgessniple.com)<br>Nationally recognized engineering and architecture design firm focused on developing practical infrastructure solutions with a passion for quality, safety, and sustainability | Civil Engineering | 🇺🇸 Columbus | 828 | 1912 |
| 38 | [GPD Group](https://www.tamtam.ai/c/gpd-group) (gpdgroup.com)<br>A multi-disciplinary firm offering architectural design, engineering, construction, telecommunications, and environmental services across various market sectors with over 700 professionals | Civil Engineering | 🇺🇸 Akron | 806 | 1961 |
| 39 | [TalentLaunch](https://www.tamtam.ai/c/talentlaunch) (mytalentlaunch.com)<br>A strategic partner for staffing firms, offering business solutions, technology, marketing, accounting, and payroll services to accelerate growth | Staffing and Recruiting | 🇺🇸 Valley View | 805 | 2016 |
| 40 | [Smithers](https://www.tamtam.ai/c/smithers) (smithers.com)<br>A multinational provider of testing, consulting, and certification services across various industries, delivering accurate data and innovative solutions through science and expertise | Research Services | 🇺🇸 Akron | 802 |  |
| 41 | [PTI](https://www.tamtam.ai/c/pti) (plastictechnologies.com)<br>Global leader in plastics packaging with expertise in preform and package design, rapid prototyping, material evaluation engineering, and package development for the industry | Packaging and Containers Manufacturing | 🇺🇸 Holland | 782 | 1985 |
| 42 | [Staffmark Group](https://www.tamtam.ai/c/staffmark-group) (smgroupna.com)<br>Specializing in staffing and recruiting across commercial, technical, and professional services, as well as process outsourcing Owned by RGF Staffing | Staffing and Recruiting | 🇺🇸 Cincinnati | 744 |  |
| 43 | [SEI](https://www.tamtam.ai/c/sei-cincinnati) (sei.com)<br>Business and technology consulting firm providing tailored solutions and cutting-edge technologies to drive powerful business results for global clients | Business Consulting and Services | 🇺🇸 Cincinnati | 722 | 1992 |
| 44 | [WD Partners](https://www.tamtam.ai/c/wd-partners) (wdpartners.com)<br>A customer experience-focused organization offering global services in strategy, brand, operations, design, architecture, engineering, and construction to drive change | Design Services | 🇺🇸 Columbus | 712 | 1968 |
| 45 | [Clark Schaefer Hackett](https://www.tamtam.ai/c/clark-schaefer-hackett) (cshco.com)<br>This company offers accounting and advisory services to clients nationwide, focusing on financial, technological, operational, and human resources support | Professional Services | 🇺🇸 Dayton | 709 | 1938 |
| 46 | [Weltman, Weinberg & Reis Co., LPA](https://www.tamtam.ai/c/weltman-weinberg-and-reis-co-lpa) (weltman.com)<br>With nearly a century of experience, this full-service law firm specializes in creditors' rights, representing major financial institutions in various legal matters | Law Practice | 🇺🇸 Cleveland | 708 | 1930 |
| 47 | [Applied Research Solutions](https://www.tamtam.ai/c/applied-research-solutions) (appliedres.com)<br>A growing company providing cyber, IT, intelligence, logistics, research, education, program management, engineering, scientific analysis, and space systems support to DoD and Intelligence Community | Defense and Space Manufacturing | 🇺🇸 Beavercreek | 695 | 2012 |
| 48 | [Tailored Management](https://www.tamtam.ai/c/tailored-management) (tailoredmanagement.com)<br>Connecting top talent with top-tier opportunities globally through our main hub in the US and international offices in Costa Rica, Philippines, and India Explore job openings on our website | Staffing and Recruiting | 🇺🇸 Columbus | 688 | 2009 |
| 49 | [Unify Healthcare Services](https://www.tamtam.ai/c/unify-healthcare-services) (unifyrcm.com)<br>A modern medical billing company specializing in revenue cycle management, claim denial prevention, and comprehensive billing solutions for healthcare facilities | Hospitals and Health Care | 🇺🇸 Cuyahoga Falls | 683 | 2016 |
| 50 | [Shumaker, Loop & Kendrick, LLP](https://www.tamtam.ai/c/shumaker-loop-and-kendrick-llp) (shumaker.com)<br>A leading provider of legal and legislative services with a large team of lawyers, paralegals, and advisors across multiple offices | Law Practice | 🇺🇸 Toledo | 669 | 1925 |

## How this list is built

Every company on this list has a Tamtam company profile. The industry is the one the company gives on LinkedIn; categories such as SaaS or fintech are classified by Tamtam's AI from the company's website and LinkedIn page; and the headquarters city must match the company's own address. Companies are ranked by the number of employees on LinkedIn, and the list is refreshed every night. Classifications can be wrong, so treat the list as a starting point rather than an official ranking. Last updated Nov 11, 2026.

## More company lists in Ohio

- [The largest companies in Ohio](https://www.tamtam.ai/l/largest-companies-ohio) (2,910)
- [Manufacturers in Ohio](https://www.tamtam.ai/l/manufacturers-ohio) (479)
- [Multinational companies in Ohio](https://www.tamtam.ai/l/multinational-companies-ohio) (390)
- [Companies with in-house R&D in Ohio](https://www.tamtam.ai/l/r-and-d-companies-ohio) (277)
- [Hardware manufacturers in Ohio](https://www.tamtam.ai/l/hardware-companies-ohio) (233)
- [Retail chains in Ohio](https://www.tamtam.ai/l/retail-chains-ohio) (230)
- [Education providers in Ohio](https://www.tamtam.ai/l/education-companies-ohio) (223)
- [Hospitals and Health Care companies in Ohio](https://www.tamtam.ai/l/hospitals-and-health-care-companies-ohio) (182)
- [Healthcare providers in Ohio](https://www.tamtam.ai/l/healthcare-providers-ohio) (181)
- [Financial services firms in Ohio](https://www.tamtam.ai/l/financial-services-firms-ohio) (162)
- [Critical infrastructure operators in Ohio](https://www.tamtam.ai/l/critical-infrastructure-operators-ohio) (153)
- [Family-owned companies in Ohio](https://www.tamtam.ai/l/family-owned-companies-ohio) (146)
- [IT Services and IT Consulting companies in Ohio](https://www.tamtam.ai/l/it-services-and-it-consulting-companies-ohio) (133)
- [Public sector organisations in Ohio](https://www.tamtam.ai/l/public-sector-organisations-ohio) (133)
- [Contract manufacturers in Ohio](https://www.tamtam.ai/l/contract-manufacturers-ohio) (122)
- [Chemical companies in Ohio](https://www.tamtam.ai/l/chemical-companies-ohio) (120)
- [IT services companies in Ohio](https://www.tamtam.ai/l/it-services-companies-ohio) (118)
- [Consulting firms in Ohio](https://www.tamtam.ai/l/consulting-firms-ohio) (115)
- [Companies with a mobile app in Ohio](https://www.tamtam.ai/l/companies-with-mobile-app-ohio) (114)
- [Higher Education companies in Ohio](https://www.tamtam.ai/l/higher-education-companies-ohio) (110)
- [Construction companies in Ohio](https://www.tamtam.ai/l/construction-companies-ohio) (109)
- [Machinery Manufacturing companies in Ohio](https://www.tamtam.ai/l/machinery-manufacturing-companies-ohio) (108)
- [Distributors and wholesalers in Ohio](https://www.tamtam.ai/l/distributors-and-wholesalers-ohio) (105)
- [Corporate groups and holding companies in Ohio](https://www.tamtam.ai/l/holding-companies-ohio) (104)

## The same list elsewhere in United States

- [Professional services firms in the United States](https://www.tamtam.ai/l/professional-services-firms-united-states) (7,078)
- [Professional services firms in New York State](https://www.tamtam.ai/l/professional-services-firms-new-york-state) (955)
- [Professional services firms in California](https://www.tamtam.ai/l/professional-services-firms-california) (880)
- [Professional services firms in Texas](https://www.tamtam.ai/l/professional-services-firms-texas) (629)
- [Professional services firms in Florida](https://www.tamtam.ai/l/professional-services-firms-florida) (375)
- [Professional services firms in Virginia](https://www.tamtam.ai/l/professional-services-firms-virginia) (344)
- [Professional services firms in Illinois](https://www.tamtam.ai/l/professional-services-firms-illinois) (339)
- [Professional services firms in Massachusetts](https://www.tamtam.ai/l/professional-services-firms-massachusetts) (249)
- [Professional services firms in New Jersey](https://www.tamtam.ai/l/professional-services-firms-new-jersey) (249)
- [Professional services firms in Georgia](https://www.tamtam.ai/l/professional-services-firms-georgia) (246)
- [Professional services firms in Pennsylvania](https://www.tamtam.ai/l/professional-services-firms-pennsylvania) (245)
- [Professional services firms in Maryland](https://www.tamtam.ai/l/professional-services-firms-maryland) (176)
- [Professional services firms in Michigan](https://www.tamtam.ai/l/professional-services-firms-michigan) (172)
- [Professional services firms in Washington State](https://www.tamtam.ai/l/professional-services-firms-washington-state) (163)
- [Professional services firms in North Carolina](https://www.tamtam.ai/l/professional-services-firms-north-carolina) (142)
- [Professional services firms in Alabama](https://www.tamtam.ai/l/professional-services-firms-alabama) (135)
- [Professional services firms in Minnesota](https://www.tamtam.ai/l/professional-services-firms-minnesota) (125)
- [Professional services firms in New York](https://www.tamtam.ai/l/professional-services-firms-new-york) (735)
- [Professional services firms in Chicago](https://www.tamtam.ai/l/professional-services-firms-chicago) (196)
- [Professional services firms in Houston](https://www.tamtam.ai/l/professional-services-firms-houston) (156)
- [Professional services firms in Atlanta](https://www.tamtam.ai/l/professional-services-firms-atlanta) (143)
- [Professional services firms in San Francisco](https://www.tamtam.ai/l/professional-services-firms-san-francisco) (130)
- [Professional services firms in Washington](https://www.tamtam.ai/l/professional-services-firms-washington) (109)
- [Professional services firms in Los Angeles](https://www.tamtam.ai/l/professional-services-firms-los-angeles) (108)

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Source: https://www.tamtam.ai/l/professional-services-firms-ohio