The Des Moines Register and the Iowa Backroads blog both have very thorough lists of post offices in Iowa that have already been closed, or which are being slated for potential closure this year. The latter link features a gallery of many of these post offices!
In 2008 I passed through the town of Thayer, Iowa and stopped by the post office. I found it undergoing what appeared to be rather extensive renovations. It was 4 p.m. Below, a USPS employee who trucked in to pick up the day's mail:
The post office of the town of 59 people is presently open three hours a day: 10:30 to 1:30 weekdays. It features two Saturday hours as well.