Grimes, IA has a population of 10,422 and is the 3,833rd largest city in the United States. The population density is 889 per sq mi which is 1527% higher than the Iowa average and 881% higher than the national average. The median age in Grimes is 33 which is approximately 14% lower than the Iowa average of 38. In Grimes, 68% of the population over 15 years of age are married, 98% speak English and 2% speak Spanish. 80% of Grimes residents were born in Iowa, 16% were born out of state, 1% were born outside of the United States and 3% were foreign born.