Caldwell, ID has a population of 50,288 and is the 811th largest city in the United States. The population density is 2,246 per sq mi which is 11674% higher than the Idaho average and 2379% higher than the national average. The median age in Caldwell is 30 which is approximately 17% lower than the Idaho average of 36. In Caldwell, 55% of the population over 15 years of age are married, 73% speak English and 26% speak Spanish. 51% of Caldwell residents were born in Idaho, 38% were born out of state, 0% were born outside of the United States and 11% were foreign born.