Waterloo, IN has a population of 2,166 and is the 10,547th largest city in the United States. The population density is 1,237 per sq mi which is 589% higher than the Indiana average and 1265% higher than the national average. The median age in Waterloo is 30 which is approximately 20% lower than the Indiana average of 37. In Waterloo, 55% of the population over 15 years of age are married, 95% speak English and 3% speak Spanish. 73% of Waterloo residents were born in Indiana, 24% were born out of state, 1% were born outside of the United States and 3% were foreign born.