I'm anticipating getting a visa requiring proof of retirement. It might be several months before I would need the income affidavit. As a US citizen, can the affidavit only be processed in Bangkok or is it possible to do at another US Embassy?

I assume you meant that you will be applying for an extension of stay at immigration here not a visa at a Thai embassy or consulate.

You have to do it at the embassy in Bangkok or the consulate in Chiang Mai.

I assume you meant that you will be applying for an extension of stay at immigration here not a visa at a Thai embassy or consulate.

You have to do it at the embassy in Bangkok or the consulate in Chiang Mai.

Yes, that was what I was referring to. Thanks much.

"You have to do it at the embassy in Bangkok or the consulate in Chiang Mai."

It can also be done at one of the ACS Outreach visits.

Check the embassy site for when and where they will be held.

The outreach visits are very handy. Here in Phuket they spend most of a day four times a year. Many USA consulate services including notary as well as the income letters. Costs are the same as at the consulate/embassy in Bangkok but best to bring the exact change in Thai baht. Can apply for passport renewals but not for adding pages.