A visual representation of the list from this article (Des Moines Register). This does NOT include the dozens targeted earlier this year. That map was heavy in north-central Iowa; here, the northwest and south get hit hard.
In many places, once you zoom in to the town, “US Post Office” is the first, or only, location that appears on the map.
EDIT: Brian McMillin has a complete list and sortable table on his website. There are now more than 250 post offices in the state at risk of closure and more than a dozen already closed.
View Post Offices July 2011 in a larger map