Mullen is located in Hooker County (of which it is the county seat), situated between Hyannis and Seneca along Hwy 2, near the Middle Loup River.
The population estimate for July 1, 1998 was 492, a decrease of 62 since 1990.
The railroad came through in 1887, and a depot named Mullen was housed in a boxcar near the Trefren trading post. The town of Mullen was established in 1888.