Willis Allen (December 15, 1806 – April 15, 1859) was a U.S. Representative from Illinois, and the father of William J. Allen. Born near Roanoke, Virginia, Allen attended the common schools. He taught school. He moved to Tennessee and settled in Wilson County. He moved to Franklin (now Williamson) County, Illinois in 1830 and engaged in agricultural pursuits. He studied law. He was admitted to the bar and commenced practice in Marion. He was sheriff of Franklin County 1834–1838. He served as member of the Illinois House of Representatives 1838–1840. He served as prosecuting attorney of the 1st judicial circuit in 1841. He served as member of the Illinois Senate 1844–1847. He served as member of the state constitutional convention in 1847 and 1848.