Colchester is a city in McDonough County, Illinois, United States. The population was 1,493 at the 2000 census. The city is named after the provincial town of Colchester, England. The Royal Grammar School in Colchester, England has clocks running at the time of Colchester, Illinois in the Geography classrooms. Colchester apartments for rent comparison page shows most up to date rent information on Colchester apartments and houses. Rent information is obtained from multiple rental sources but we cannot guarantee their accuracy.