Check your tax return documents
Look at prior IRS or tax agency notices
Review your Social Security card or tax registration records
Check your employer’s payroll or tax forms
Log in to your IRS or tax authority online account
Contact your accountant, tax preparer, or payroll department
Call the IRS or your local tax authority
Search business formation or registration paperwork
Check bank, loan, or licensing documents that may list it
Request a replacement or confirmation from the relevant tax authority