Round Rock, TX has a population of 112,767 and is the 250th largest city in the United States. The population density is 3,144 per sq mi which is 3143% higher than the Texas average and 3370% higher than the national average. The median age in Round Rock is 33 which is approximately 3% lower than the Texas average of 34. In Round Rock, 56% of the population over 15 years of age are married, 72% speak English and 20% speak Spanish. 53% of Round Rock residents were born in Texas, 32% were born out of state, 2% were born outside of the United States and 14% were foreign born.