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.

Iola is the county seat of Allen County, Kansas, United States. The city is situated along the Neosho River in southeast Kansas. As of the 2020 census, the population of the city was 5,396. It is named in honor of Iola Colborn, the wife of Josiah Colborn, one of the town's founders.