Letter proof of residency - (Non immigration related...)?

poster one is correct -- send them a copy of one of your utility bills showing name and address!!!

I have never heard of a letter as proof of residency so I'm unsure to come about it but alot of state governments and such have the following guidelines.

To show proof of residency, you have a variety of options to prove your current address. Examples include a recent utility bill (including phone, electric, gas, water, sewer, and cable), property tax receipt, or most recent bank statement, voter ID card, or any official letter issued within the last 30 days by another state or local governmental agency on its letterhead. Proof of residency will be required each time you apply to renew a driver license, nondriver license, or instruction permit. A complete list of documents that will be accepted as proof of residency is available. If you are under the age of 21 and cannot provide proof of residency, a parent or legal guardian may provide such a document on your behalf.

* Resident address is the location at which a person has been physically present and regards as home. A residence address is a person's true, fixed, principal, and permanent home, to which a person intends to return and remain, even though currently residing elsewhere.

I hope this helps

Usually, proof of residency involves a photo ID from some government organization. Consider a driving license, medical card, or some other item with your name and address clearly shown. I have never heard of writing a letter for proof of residency.