According to the 2001 census Kilsby had a population of 1,221. The village has grown considerably since the 1960s, with several new housing developments and a degree of in-filling. Amenities include a primary school, post office and shop, two pubs and two churches - Church of England and URC.
Kilsby's name comes from Anglo-Saxon cildes + old Norse býr, literally meaning "child's dwelling", but "child" here probably means "young nobleman". Its church, St Faith's, may originally have been the daughter chapel of the neighbouring parish of Barby.
The parish's eastern side is bounded by the old route of the Roman Watling Street, and the village itself is sited on the crossing of two former mediaeval drove-routes. It gives its name to the Kilsby Tunnel on the West Coast Main Line. The tunnel measures 1 mile 666 yards (2,216 m). Between 1881 and 1960, the village used to have a railway station Kilsby and Crick station but this was on the Northampton Loop further away from the village.