Onion Creek is a census-designated place in Travis County, Texas, United States. The population was 2,116 at the 2000 census. Onion Creek is also the name of a creek that starts in Hays County, Texas and empties into the Colorado River. Onion Creek apartments for rent comparison page shows most up to date rent information on Onion Creek apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.