Check your IRS EIN confirmation letter
Review prior tax returns and business filings
Look at bank account opening documents for your business
Check payroll, vendor, or licensing records
Search your business email for IRS correspondence
Call the IRS Business & Specialty Tax Line at 800-829-4933
Ask your accountant, bookkeeper, or attorney
Log in to your business tax or payroll software
Check state business registration records if the EIN was filed there