Write a letter to a state agency, like the DMV, or voter registration, that will require an answer from them. Fill out an official affidavit form and sign it in the presence of a notary.If you need a proof of residency letter, you can print this free proof of residency letter template and fill in the necessary information. Don't have utility bills? They do have an extended list of options you can use to prove residency. A valid DC driver's license or non-driver's ID card. - A valid lease, rental agreement, rent receipt, deed, settlement papers, or mortgage statement for.