Postville is a city in Allamakee and Clayton Counties in the U.S. state of Iowa. It lies near the junction of four counties and at the intersection of U.S. Routes 18 and 52 and Iowa Highway 51, with airport facilities in the neighboring communities of Waukon, Decorah, Monona, and Prairie du Chien. The population was 2,227 at the 2010 census, down from 2,273 The city is located in the southwestern corner of Allamakee County and the northwestern corner of Clayton County in a quad county or four corner region where four counties meet in the same spot.