Posey County is the southernmost, southwesternmost, and westernmost county in the U.S. state of Indiana. Its southern border is formed by the Ohio River, and its western border by the Wabash River, a tributary to the Ohio. As of 2020, the population was 25,222. The county seat is Mount Vernon.

Union County is a county in the U.S. state of Kentucky. As of the 2020 census, the population was 13,668. Its county seat is Morganfield. The county was created effective January 15, 1811.