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.
| # | Company | Employees | |||
|---|---|---|---|---|---|
| 1 |
Staffmarkstaffmark.com
Staffing company focused on matching jobs with exceptional people, delivering top customer satisfaction with industry-leading service quality Join us today! |
8,923 | |||
| 2 | 8,651 | ||||
| 3 |
Medpacemedpace.com
Global CRO accelerating drug, biologic, and medical device clinical development through high-science expertise in various therapeutic areas worldwide |
6,421 | |||
| 4 |
AML RightSourceamlrightsource.com
Provides trained professionals for Anti-Money Laundering, Bank Secrecy Act, and financial crimes compliance, including transaction monitoring and due diligence. |
6,341 | |||
| 5 |
Battellebattelle.org
A science and technology company solving critical issues through research, development, manufacturing, and services for government and commercial clients worldwide |
6,013 | |||
| 6 |
Belcanbelcan.com
Global provider of engineering, manufacturing, workforce, and IT solutions for aerospace, defense, automotive, industrial, and private sector clients for over 60 years |
5,115 | |||
| 7 |
Squire Patton Boggssquirepattonboggs.com
A global law firm with over 1,500 lawyers across four continents, providing legal insight and support for businesses in various sectors |
3,630 | |||
| 8 | 2,949 | ||||
| 9 |
Taft Stettinius & Hollister LLPtaftlaw.com
A client-focused legal and government affairs consulting firm offering innovative solutions and advocacy at federal, state, and local levels |
2,217 | |||
| 10 |
RDI Corporationrdicorp.com
A comprehensive business solutions provider offering customized outsourced services including contact center, IT, market research, and digital strategy support |
1,947 | |||
| 11 |
Woolpertwoolpert.com
A global architecture, engineering, geospatial, and strategic consulting firm serving public, private, and government clients worldwide with a focus on innovation and growth |
1,843 | |||
| 12 |
RoviSysrovisys.com
An independent control system integrator offering comprehensive process automation solutions and services with a focus on open systems and client choices |
1,841 | |||
| 13 |
Nesco Resourcenescoresource.com
Connecting companies with talent, candidates with opportunities through flexible staffing solutions including contract, contract-to-hire, and direct placement services. |
1,759 | |||
| 14 |
Dinsmore & Shohl LLPdinsmore.com
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 |
1,719 | |||
| 15 | 1,659 | ||||
| 16 |
SSOE Groupssoe.com
Internationally recognized architecture and engineering firm specializing in providing high-quality project solutions for various industries with global reach |
1,634 | |||
| 17 |
Davey Resource Group, Inc.davey.com
The company provides innovative solutions and expertise to a diverse range of clients in industries such as utilities, transportation, telecommunications, and government |
1,605 | |||
| 18 |
FBT Gibbonsfbtgibbons.com
A nationwide law firm with over 575 attorneys providing expert legal advice and representation in a variety of industries across the United States |
1,536 | |||
| 19 |
The Planet Grouptheplanetgroup.com
A diversified organization providing human capital solutions and consulting services to Fortune 500 clients in technology, energy, finance, HR, administrative, and marketing industries |
1,417 | |||
| 20 |
Hylanthylant.com
A leading full-service insurance brokerage with nationwide presence, offering risk management, employee benefits, wellness strategies, insurance solutions for businesses and individuals |
1,329 | |||
| 21 |
Part Time WorksPartTimeWorks.com
Specializing in part-time professional placement services, we connect job seekers with organizations seeking efficient, effective part-time staffing solutions for long-term employment |
1,169 | |||
| 22 |
Centric Consultingcentricconsulting.com
Provides AI strategy, cyber risk management, cloud solutions, and tailored consulting services with experienced advisors and scalable teams. |
1,159 | |||
| 23 |
Advantage Resourcingadvantageresourcing.com
An experienced recruitment company offering talent placement in various industries and stages of career, with global reach and comprehensive services |
1,087 | |||
| 24 |
CBIZ Advisory Servicescbiz.com
A financial services division providing accounting, tax, consulting, audit, and industry-specific services to clients nationwide, in collaboration with an independent CPA firm |
1,055 | |||
| 25 |
Cohen & Cocohenco.com
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 |
1,045 | |||
Want more companies than this list?This page shows the largest ones only. Connect to Tamtam to see every company that matches, filter by size, industry or growth, and reach their decision-makers. | |||||
| 26 |
E Tech Groupetechgroup.com
A leading engineering and system integration firm providing automation solutions to various industries with a team of over 450 engineers |
1,010 | |||
| 27 |
Advantage Technicaladvantagetechnical.com
This company specializes in aligning individuals with job opportunities that match their experience, skills, motivation, and goals |
986 | |||
| 28 |
Health Carouselhealthcarousel.com
A total talent management company providing healthcare staffing solutions to ensure US patients have access to qualified professionals when needed |
984 | |||
| 29 |
Benesch Lawbeneschlaw.com
Provides sophisticated legal services to national and international public and private companies, private equity funds, entrepreneurs, and not-for-profit organizations. |
949 | |||
| 30 |
Thompson Hine LLPthompsonhine.com
A leading full-service business law firm known for innovation, offering efficient, client-focused legal services through Thompson Hine SmartPaTH庐 |
933 | |||
| 31 |
DLZ Corporationdlz.com
A top consulting firm in architecture/engineering, DLZ works on projects nationwide, focusing on client service, innovation, and turning visions into reality |
911 | |||
| 32 |
GPRSgp-radar.com
The company specializes in damage prevention, data collection, existing condition documentation, and facility & project management using innovative technology and software solutions |
894 | |||
| 33 |
Lisinski Law Firmlisinskifirm.com
Dedicated attorneys provide nationwide legal representation for immigration cases, advocating for client rights and compassionate support to remain with family |
880 | |||
| 34 |
The Reserves Networktrnstaffing.com
Provides personalized staffing services across multiple industries, placing temporary, temporary-to-hire, and direct-hire employees nationwide. |
876 | |||
| 35 |
Crown Staffingcrownstaffing.com
A staffing company providing innovative personnel solutions to companies and individuals in the Midwest and southern United States since 1968 |
873 | |||
| 36 |
Vorys, Sater, Seymour and Pease LLPvorys.com
A pioneering firm providing innovative solutions for clients for over 100 years, with a team of 375 attorneys across 10 offices worldwide |
869 | |||
| 37 |
Burgess & Nipleburgessniple.com
Nationally recognized engineering and architecture design firm focused on developing practical infrastructure solutions with a passion for quality, safety, and sustainability |
828 | |||
| 38 |
GPD Groupgpdgroup.com
A multi-disciplinary firm offering architectural design, engineering, construction, telecommunications, and environmental services across various market sectors with over 700 professionals |
806 | |||
| 39 |
TalentLaunchmytalentlaunch.com
A strategic partner for staffing firms, offering business solutions, technology, marketing, accounting, and payroll services to accelerate growth |
805 | |||
| 40 |
Smitherssmithers.com
A multinational provider of testing, consulting, and certification services across various industries, delivering accurate data and innovative solutions through science and expertise |
802 | |||
| 41 |
PTIplastictechnologies.com
Global leader in plastics packaging with expertise in preform and package design, rapid prototyping, material evaluation engineering, and package development for the industry |
782 | |||
| 42 |
Staffmark Groupsmgroupna.com
Specializing in staffing and recruiting across commercial, technical, and professional services, as well as process outsourcing Owned by RGF Staffing |
744 | |||
| 43 | 722 | ||||
| 44 |
WD Partnerswdpartners.com
A customer experience-focused organization offering global services in strategy, brand, operations, design, architecture, engineering, and construction to drive change |
712 | |||
| 45 |
Clark Schaefer Hackettcshco.com
This company offers accounting and advisory services to clients nationwide, focusing on financial, technological, operational, and human resources support |
709 | |||
| 46 |
Weltman, Weinberg & Reis Co., LPAweltman.com
With nearly a century of experience, this full-service law firm specializes in creditors' rights, representing major financial institutions in various legal matters |
708 | |||
| 47 |
Applied Research Solutionsappliedres.com
A growing company providing cyber, IT, intelligence, logistics, research, education, program management, engineering, scientific analysis, and space systems support to DoD and Intelligence Community |
695 | |||
| 48 |
Tailored Managementtailoredmanagement.com
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 |
688 | |||
| 49 |
Unify Healthcare Servicesunifyrcm.com
A modern medical billing company specializing in revenue cycle management, claim denial prevention, and comprehensive billing solutions for healthcare facilities |
683 | |||
| 50 |
Shumaker, Loop & Kendrick, LLPshumaker.com
A leading provider of legal and legislative services with a large team of lawyers, paralegals, and advisors across multiple offices |
669 | |||
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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.
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The same list elsewhere in United States
- Professional services firms in the United States 7,078
- Professional services firms in New York State 955
- Professional services firms in California 880
- Professional services firms in Texas 629
- Professional services firms in Florida 375
- Professional services firms in Virginia 344
- Professional services firms in Illinois 339
- Professional services firms in Massachusetts 249
- Professional services firms in New Jersey 249
- Professional services firms in Georgia 246
- Professional services firms in Pennsylvania 245
- Professional services firms in Maryland 176
- Professional services firms in Michigan 172
- Professional services firms in Washington State 163
- Professional services firms in North Carolina 142
- Professional services firms in Alabama 135
- Professional services firms in Minnesota 125
- Professional services firms in New York 735
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- Professional services firms in Houston 156
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- Professional services firms in San Francisco 130
- Professional services firms in Washington 109
- Professional services firms in Los Angeles 108