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.

Domesday Book records four manors, or holdings in Northill. Two of these were held by Eudo the Steward, also known as Eudo, son of Hubert, who had twenty seven manors in Bedfordshire and other manors in other counties. Both his Northill estates comprised one and a half hides. One was tenanted by a man named Pirot, then other by a man named Ralph.

Pirot's holding had three villagers and a smallholder and a mill worth fourteen shillings. This would have been a watermill as there were no windmills in England at that date. This suggests that the manor may have been in the east of the parish and that the mill stood on the River Ivel. The Victoria County History for Bedfordshire identifies this holding with Caminos alias Lower Caldecote Manor.

Pirot's manor had belonged to a man named Raven in 1066, who had it from Wulfmer of Eaton, a thegn of King Edward the Confessor. It had then been worth twenty five shillings. This value had decreased to ten shillings by the time Eudo acquired it, though it had risen to twenty shillings by 1086. It is suggested by historians that the reason for the general lowering of the value of manors in the area is accounted for by William I's armies coming through Bedfordshire on their way to put down rebellions in the north. They would have lived off the land and no doubt have committed certain acts of vandalism in what was, to them, still alien, even enemy, territory.

Ralph's manor had five smallholders and three slaves as well as woodland for a hundred pigs. It had been worth sixty shillings in 1066, when it belonged to two freemen. The value had been forty shillings when Eudo acquired it but was £3 in 1086. The Victoria County History for Bedfordshire states that this land lay in Ickwell and later became Ickwell Manor.

The third manor belonged to Hugh de Beauchamp, who would later be created Baron of Bedford. His tenant was a man named Walter and the manor comprised just half a hide, with no villagers, smallholders or slaves. A man named Osgeat had held it in 1066 when it had been worth ten shillings, though this had been halved by the time Hugh acquired it and remained at five shillings in 1086.

The last manor was held by William Speke or Espec and was by far the largest at six and a half hides and William had no tenant. There were ten villagers and four slaves as well as half a mill, valued at thirteen shillings and woodland for two hundred pigs. In 1066 six freemen had held the manor and it had been worth £8, falling to £6 when Speke acquired it and remaining at that level in 1086. This later became known as Northill Manor.

Altogether, then, Northill comprised thirteen villagers, six smallholders and seven slaves - a total of twenty six heads of household. This figure should be multiplied by a factor of at least four to allow for wives and children suggesting a total population of a little over a hundred, a reasonably sized settlement for the time, although dispersed across the parish in a number of settlements, just as today.