Spencer County is a county located in the U.S. state of Kentucky. As of the 2020 census, the total population was 19,490. Its county seat is Taylorsville. The county was founded in 1824 and named for Spier Spencer.

Bullitt County is a county located in the north central portion of the U.S. state of Kentucky. As of the 2020 census, the population was 82,217. Its county seat is Shepherdsville. The county was founded in 1796. Located just south of the city of Louisville, Bullitt County is included in the Louisville/Jefferson County, KY-IN Metropolitan Statistical Area, commonly known as Kentuckiana. The western fifth of the county is part of the United States Army post of Fort Knox and is reserved for military training.