Williamsburg, IA has a population of 3,144 and is the 8,572nd largest city in the United States. The population density is 841 per sq mi which is 1439% higher than the Iowa average and 828% higher than the national average. The median age in Williamsburg is 38 which is approximately 1% higher than the Iowa average of 38. In Williamsburg, 73% of the population over 15 years of age are married, 96% speak English and 3% speak Spanish. 89% of Williamsburg residents were born in Iowa, 10% were born out of state, 0% were born outside of the United States and 1% were foreign born.