Check tax documents, such as prior returns, W-2s, 1099s, or IRS notices
Look on business formation records, licenses, or registration documents
Search state or local business registries if it is a business tax ID
Contact the IRS if you need to verify a federal EIN
Contact your state tax agency for a state tax ID
Ask the business or individual directly for their tax ID
Use official online lookup tools provided by tax authorities where available
Review bank, payroll, or accounting records if you have authorized access
Consult a tax professional or attorney if you are legally entitled to obtain it