Ennis is a city in eastern Ellis County, Texas, United States. The population is 20,159 according to the 2020 census, with an estimate…Ennis is a city in eastern Ellis County, Texas, United States. The population is 20,159 according to the 2020 census, with an estimated population of 23,686 in 2023. Ennis is home to the annual National Polka Festival.