Round Rock, AZ has a population of 861 and is the 16,098th largest city in the United States. The population density is 60 per sq mi which is 5% higher than the Arizona average and 33% lower than the national average. The median age in Round Rock is 26 which is approximately 31% lower than the Arizona average of 37. In Round Rock, 43% of the population over 15 years of age are married, 16% speak English and 0% speak Spanish. 87% of Round Rock residents were born in Arizona, 13% were born out of state, 0% were born outside of the United States and 0% were foreign born.