Professional Services Companies in Illinois: 93 Verified Firms
Secwyn has verified 93 professional services companies based in Illinois. The largest groups are Engineering Services (31); Temporary Help Services (21); and Employment Placement Agencies (17). By headcount, 71% have 51–200 employees, 18% have 201–500 employees, and 11% fall in other size bands. Size is not yet confirmed for 4. Chicago has the most (34), followed by Hinsdale (3) and Itasca (3).
Company size
- 11–50 employees2 · 2%
- 51–200 employees63 · 68%
- 201–500 employees16 · 17%
- 501–1,000 employees8 · 9%
- Size not confirmed4 · 4%
Top cities
- Chicago34 · 37%
- Hinsdale3 · 3%
- Itasca3 · 3%
- Northbrook3 · 3%
- St. Charles3 · 3%
Cities with fewer than 3 companies are not listed.
Largest sub-industries
| Sub-industry | NAICS | Companies |
|---|---|---|
| Engineering Services | 541330 | 31 |
| Temporary Help Services | 561320 | 21 |
| Employment Placement Agencies | 561311 | 17 |
| Architectural Services | 541310 | 11 |
| Landscaping Services | 561730 | 3 |
| Executive Search Services | 561312 | 2 |
| Materials Recovery Facilities | 562920 | 2 |
| Remediation Services | 562910 | 2 |
A sample of these companies
A few of the 93 professional services companies in Illinois. Names, websites and contacts are shown after you sign up.
Company #1 · name shown after sign-up
Engineering Services · 51–200 employees · St. Charles
Company #2 · name shown after sign-up
Employment Placement Agencies · 51–200 employees · Chicago
Company #3 · name shown after sign-up
Janitorial Services · 51–200 employees · Chicago
Company #4 · name shown after sign-up
Temporary Help Services · 501–1,000 employees
Company #5 · name shown after sign-up
Offices of Certified Public Accountants · 201–500 employees · Chicago
Company #6 · name shown after sign-up
Landscaping Services · 51–200 employees
Find the Illinois professional services companies that fit what you sell
Describe what you sell and Secwyn shows the companies most likely to buy it, with the reasons for each match. Sign up free and your first 3 company reveals are on us: name, website, description with its source, contact channels and the roles to contact.
How Secwyn verifies these companies
- Every company description is a sentence visible on the company's own website. Inside the product, each one links to its source page.
- Each company has a NAICS industry code, the US government standard for classifying businesses.
- All companies are based in the United States. Location and size come from public sources, including company filings and People Data Labs.
Data updated October 6, 2026.