Garrison, IA has a population of 352 and is the 21,574th largest city in the United States. The population density is 1,427 per sq mi which is 2512% higher than the Iowa average and 1475% higher than the national average. The median age in Garrison is 41 which is approximately 8% higher than the Iowa average of 38. In Garrison, 69% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 90% of Garrison residents were born in Iowa, 10% were born out of state, 0% were born outside of the United States and 0% were foreign born.