Colchester, IL has a population of 1,492 and is the 12,719th largest city in the United States. The population density is 1,495 per sq mi which is 572% higher than the Illinois average and 1550% higher than the national average. The median age in Colchester is 40 which is approximately 8% higher than the Illinois average of 37. In Colchester, 53% of the population over 15 years of age are married, 98% speak English and 0% speak Spanish. 87% of Colchester residents were born in Illinois, 11% were born out of state, 0% were born outside of the United States and 2% were foreign born.