Ongar is recorded in the Domesday Book and was evidently an important centre as both the hundredal moot and the hundredal market were held there. Ongar Great Park to the west of the town is the oldest recorded park in England, being first mentioned in an Anglo-Saxon will of 1015. Chipping Ongar castle was constructed in the decades following the Conquest, becoming the main manor of the Boulogne estates. The town appears to have been a deliberate plantation attached to the castle. The church, which is an integral part of the town plan is thought to date to the mid-12th century. The market is first mentioned in 1287, but was probably a direct successor to the hundredal market. The 1377 poll-tax records 108 tax-payers in Chipping Ongar.
Chipping Ongar appears to have become a significant staging-point for travellers in the early post-medieval period, and by 1686 there was within the town accommodation for 71 people and 104 horses. The taxation data for 1801 records a population of 595, rising in 1841 to a population of 870. However the main period of growth has been as a commuter town in the second half of the 20th century.