Ennis is a city in eastern Ellis County, Texas, United States, located south of Dallas. The population was 18,513 at the 2010 census, up from 16,454 at the 2000 census. It is the third largest city in Ellis County with the county seat Waxahachie being the most populous, followed by the city of Midlothian. The city is also home to the National Polka Festival.Ennis is located in the southeastern portion of the Dallas-Fort Worth Metroplex.