Stephenville, TX has a population of 18,387 and is the 2,341st largest city in the United States. The population density is 1,547 per sq mi which is 1506% higher than the Texas average and 1607% higher than the national average. The median age in Stephenville is 25 which is approximately 27% lower than the Texas average of 34. In Stephenville, 42% of the population over 15 years of age are married, 87% speak English and 12% speak Spanish. 72% of Stephenville residents were born in Texas, 23% were born out of state, 1% were born outside of the United States and 4% were foreign born.