You can search for Illinois businesses three ways. The fastest is the free CompanyData.com lookup tool at the top of this page. Type a company name and get instant results including address, registration number, entity type, and revenue estimates. You can also search the official Illinois Secretary of State at https://apps.ilsos.gov/businessentitysearch/ for authoritative filing status. For developers, our API provides programmatic access to all IL business records for bulk lookup, KYB verification, and CRM enrichment.
Free Illinois business records search
Chicago is home to 36 Fortune 500 headquarters. Illinois is a major hub for finance and manufacturing. CompanyData.com gives you instant access to IL company records. Search by company name or registration number to find addresses, entity types, founding dates, industry classifications, and revenue estimates. Our database covers active and inactive entities filed with the Illinois Secretary of State's office, plus enriched data fields not available in the official state filing system.
Illinois has the 5th largest economy of any US state. The IL economy is driven by finance, manufacturing, agriculture, and transportation, and our database tracks businesses across all of these sectors. Whether you're verifying a vendor, prospecting new leads, or running a KYB check, you can pull complete IL company profiles in seconds.
This is a faster, more data-rich alternative to searching the official Illinois Secretary of State portal directly. You get the same registry data plus revenue estimates, employee counts, SIC and NAICS codes, corporate hierarchy, and bulk CSV export, all in one search. You can also search across all Illinois entity types including Series LLC, Limited Worker Cooperative Association.
Top Companies in Illinois
Largest Illinois business entities by revenue. Includes IL finance, manufacturing, agriculture companies and more.
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How to look up a business in Illinois
There are three ways to search for Illinois business entities:
Use the free CompanyData.com tool above
Type a company name and get instant results. We aggregate Illinois business records from the Illinois Secretary of State and enrich them with revenue estimates, employee counts, and SIC/NAICS industry classifications that the official IL filing system does not provide.
Search the official Illinois Secretary of State
Visit https://apps.ilsos.gov/businessentitysearch/ for the authoritative state filing record. This is slower than CompanyData.com but provides direct access to official filing documents.
Use the CompanyData.com API
Developers can pull Illinois business records programmatically for KYB verification, lead enrichment, CRM auto-fill, and bulk data export. From $0.10 per call.
What you can find in Illinois business records
Illinois Secretary of State registry data
- Registered business name
- Entity type (LLC, Corp, LP, Series LLC, etc.)
- Registration / filing number
- Filing date & status (active/inactive)
- Registered agent & principal address
Enriched IL data (CompanyData.com)
- Revenue estimates & employee counts
- Industry classification (SIC & NAICS) for Illinois's finance, manufacturing sectors and more
- Corporate hierarchy & parent company
- Email & phone (with data license)
- Website & trade names
- Bulk export to CSV
Illinois Business Entity Types
Illinois recognizes all standard US business entity types. Whether you're starting a finance company or a professional services firm, the right structure depends on your liability protection needs, tax treatment, and growth plans. Here are the entity types you'll find when searching Illinois business records:
- Limited Liability Company (LLC): The most popular entity type for new Illinois businesses. The Illinois LLC filing fee is $150. LLCs offer personal liability protection with pass-through taxation and minimal compliance requirements.
- Corporation (C-Corp / S-Corp): C-Corps are taxed at the entity level and are the standard structure for venture-backed startups and companies planning to issue stock or go public. S-Corps elect pass-through taxation but are limited to 100 shareholders. Filing fee: $150.
- Limited Partnership (LP): A partnership with one or more general partners (who manage the business and bear unlimited liability) and limited partners (who invest but have limited liability). LPs are common in Illinois's financial sector, especially real estate, private equity, and investment fund structures.
- Limited Liability Partnership (LLP): Used primarily by professional service firms such as law, accounting, medicine, and architecture practices. In an LLP, all partners have limited liability for the firm's debts and the actions of other partners. LLPs are widely used across Illinois's financial services industry.
- Nonprofit Corporation: Organized for charitable, educational, religious, or scientific purposes. Eligible for federal tax-exempt status under IRC Section 501(c)(3) after IRS approval. Illinois nonprofits file with the Illinois Secretary of State and must comply with state-specific reporting requirements.
- Series LLC: Illinois is one of the states that allows Series LLCs, where a single LLC can create separate "series" with distinct assets, liabilities, and members without forming separate legal entities. This is popular for real estate investors holding multiple properties.
- Limited Worker Cooperative Association: A specialized entity type recognized in Illinois. Check with the Illinois Secretary of State for specific formation requirements and ongoing obligations.
Illinois Filing Fees and Requirements
Forming a business entity in Illinois requires filing with the Illinois Secretary of State and paying a one-time formation fee. Annual maintenance requirements vary by entity type.
LLC Formation
$150Filing feeCorporation
$150Filing feeAnnual Report
$75Annual feeKey facts about Illinois businesses
- Chicago is home to 36 Fortune 500 headquarters
- Illinois has the 5th largest economy of any US state
Common reasons to look up an Illinois business
KYB / Compliance Verification
Verify Illinois businesses before onboarding customers, vendors, or partners. Confirm that a IL entity is actively registered with the Illinois Secretary of State, check its entity type, and validate its filing history.
Sales Prospecting
Find Illinois companies matching your ideal customer profile. Target IL's finance and manufacturing sectors by filtering on SIC/NAICS industry code, revenue range, employee count, or location. Export matching Illinois companies to CSV for outreach.
Vendor Due Diligence
Before signing contracts or sending payments, confirm that an Illinois vendor is a real, registered, active entity. You can verify registration status, formation date, and registered agent details in seconds.
Market Research
Analyze Illinois's finance, manufacturing, and agriculture landscape. Count businesses by sector, identify market leaders, benchmark competitors by revenue and employee count, and track industry concentration across IL regions.
Background Checks
Look up the corporate history of any Illinois entity: formation date, name changes, mergers, and dissolution records. Check whether annual reports have been filed and whether the entity is in good standing with the Illinois Secretary of State.
Lead Enrichment
Enrich your CRM with Illinois company data via the CompanyData.com API. Append revenue estimates, employee counts, SIC/NAICS industry codes, and corporate hierarchy to your existing IL contacts. From $0.10 per enrichment call.
Automate these lookups with our API
Send a company name or number, get the same records back as structured JSON. Classify a whole list in one run instead of searching them one by one. Every new key starts with 500 free lookups.
Just need a ready-made company database?
No integration, no code. The same enriched register as a ready-made Excel or CSV file: pick your SIC codes, regions and sizes, and get a free sample first.
Frequently asked questions about Illinois business search
Illinois business records include the registered company name, entity type (LLC, Corporation, LP, etc.), filing status (active/inactive), formation date, registered agent, principal business address, and registration number. CompanyData.com enriches these records with fields you won't find in the state filing system: estimated revenue, employee count, SIC/NAICS industry classification, corporate hierarchy, and parent company linkage. This is especially useful for researching Illinois's finance and manufacturing sectors.
The standard Illinois LLC filing fee is $150, paid to the Illinois Secretary of State.. Illinois also requires an annual report with a $75 fee.
Filing Articles of Incorporation in Illinois costs $150, paid to the Illinois Secretary of State. Corporations must also file annual reports to maintain good standing.
Illinois business records list the registered agent and, in some cases, directors or members of record. However, the Illinois Secretary of State filing system rarely shows the ultimate beneficial owner. For full ownership data including UBO (Ultimate Beneficial Owner) information and corporate hierarchy, use the CompanyData.com API, which combines IL registry data with ownership records from multiple sources.
An active Illinois business is in good standing, meaning its filings are current and it can legally conduct business in IL. Inactive (dissolved, suspended, or forfeited) entities cannot transact. In Illinois, entities that fail to file annual reports or pay franchise taxes can be administratively dissolved or suspended by the Illinois Secretary of State. CompanyData.com shows both active and inactive entities so you can verify a company's full history.
Yes. The CompanyData.com IL business lookup at the top of this page is free with no signup required. The official Illinois Secretary of State portal is also free to search. CompanyData.com is faster and includes enriched fields (revenue, employees, SIC/NAICS codes) that the state portal does not provide. For bulk access or API integration, paid plans start at $0.10 per lookup.
Illinois recognizes Limited Liability Companies (LLCs), Corporations (C-Corp and S-Corp), Limited Partnerships (LPs), Limited Liability Partnerships (LLPs), General Partnerships, Sole Proprietorships, and Nonprofit Corporations. Illinois also recognizes Series LLC, Limited Worker Cooperative Association, which are not available in every state. You can search for any of these entity types using the lookup tool above.
An Employer Identification Number (EIN) is issued by the IRS, not by Illinois. After forming your IL entity with the Illinois Secretary of State, apply for an EIN for free at irs.gov.
The official Illinois business filing portal is maintained by the Illinois Secretary of State at https://apps.ilsos.gov/businessentitysearch/. CompanyData.com offers a faster search experience with additional data fields like revenue estimates and industry classification that the state portal does not include.
CompanyData.com refreshes IL business records daily from official Illinois Secretary of State filings. Revenue, employee, and corporate hierarchy data is updated on a rolling basis from multiple sources. The official state system is updated in real time as filings are submitted.
Yes, CompanyData.com supports CSV export of IL business records and provides a REST API for programmatic bulk access. This is used for sales prospecting, lead enrichment, KYB verification, and market research. Filter by Illinois's key industries (Finance, Manufacturing, Agriculture), revenue range, employee count, or entity type.