Fremont County is a county located in the U.S. state of Iowa. As of the 2020 census the population was 6,605, making it the state's seventh-least populous county. The county seat is Sidney. The county was formed in 1847 and named for the military officer John C. Frémont.

Mills County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 14,484. The county seat is Glenwood. The county was formed in 1851 and named for Major Frederick Mills of Burlington, Iowa who was killed at the Battle of Churubusco during the Mexican–American War.