Start looking for an old bank account number by going through the old papers that you have stored in your home. If you have kept most of your old financial papers, you will likely have the number somewhere. Look not only at old bank account documents, but also at old loan papers, old rental agreements and past tax returns. Loan paperwork almost always requires bank account information; occasionally rental applications do, and tax returns may contain account information if you have used the direct deposit option in the past.
Look for old check registers. If you find old check registers when looking through paperwork, the account number will be listed at the bottom of the checks. The account number isgenerally the second set of numbers to the right of the routing number.
Write a short letter that can be sent to the bank. Include as much information as possible in the letter. Since you do not know the account number, which is the main method that banks use to keep track of accounts, you will need to provide enough identifying information to ensure the bank's management that you were the account holder. Include your first and last name, Social Security number, birth date and the address where you lived when the bank account was open. The bank should have had all of this information on file.
Send the letter into the bank where you had the account. Each bank has its own ownership and keeps its own records, so you will need to contact the bank directly. You can find the bank address on the bank's website or in the phone book if you are sending the letter to a local branch.