Domesday Book was commissioned by William the Conqueror (1066-1087) at Christmas 1085. It was designed to show who held every piece of land in the newly conquered Kingdom of England. It was known colloquially as the Domesday Book because it was seen as being as final as the Last Judgement and as difficult to conceal things from. The book does not cover the whole country - Cumberland, Durham, Northumberland, and Westmorland were omitted and London and Winchester likewise, along with some other towns. A separate book, called Little Domesday covered the counties of Essex, Norfolk and Suffolk and, despite its name, it is actually bigger and more detailed than the Great Domesday Book containing the other counties.

Ridgmont is not mentioned in Domesday Book, rather it is Segenhoe, the original settlement, which is listed. It was one of two manors in the county owned by Walter, brother of Sihere. It comprised ten hides and had twenty four villagers, four smallholders and three slaves. These thirty one people were the heads of household and to arrive at a more realistic number of inhabitants one therefore needs to multiply this figure by at least four. This suggests a population in excess of a hundred and twenty, making Ridgmont a fair sized community, larger, for example, than Aspley Guise.

A man named Leofnoth, a thegn of King Edward the Confessor had held the manor in 1066, though a freeman had half a hide of it himself and could buy and sell independently of Leofnoth. Ridgmont had then been worth £16. When Walter acquired the manor it was worth £10 and the value had shrunk to £6 by 1086. It has been suggested that the reason for such substantial falls in value in parts of Bedfordshire was due to the depredations of William the Conqueror's armies as they moved north to subdue rebellion.