Neosho County is a county located in Southeast Kansas. Its county seat is Erie. As of the 2020 census, the county population was 15,904. The county was named for the Neosho River, which passes through the county.

Allen County is a county located in the southeast portion of the U.S. state of Kansas. Its county seat and most populous city is Iola. As of the 2020 census, the population was 12,526. The county was named for William Allen, a U.S. Senator from Ohio and prominent supporter of westward expansion.