Killeen, TX has a population of 138,745 and is the 192nd largest city in the United States. The population density is 2,561 per sq mi which is 2542% higher than the Texas average and 2727% higher than the national average. The median age in Killeen is 28 which is approximately 18% lower than the Texas average of 34. In Killeen, 57% of the population over 15 years of age are married, 78% speak English and 15% speak Spanish. 35% of Killeen residents were born in Texas, 48% were born out of state, 8% were born outside of the United States and 9% were foreign born.