St Leonard's has a four-bay clerestoreyed nave, the arcades divided into two two-bay sections by a short stretch of wall. In the N arcade all the arches are pointed and the capitals moulded; in the S the E bays are similar, but the W bays have round arches. Nevertheless both arcades are 13thc., but for two features. The base of N pier 3 is a reused, inverted multi-scallop pier capital (or, as Pevsner suggests, a pair of respond capitals), and chevron voussoirs have been cut down for reuse in the E arches of the S arcade. For the rest, the chancel is 13thc. and there is a low W tower, late 13thc. in its lower parts and Perpendicular above.

Glapthorn is not mentioned in the Domesday Survey. Nothing is known of the manor's ownership until Robert Brudenell acquired it in 1512. It has remained in the possession of his successors.

Benefice of Oundle with Ashton and Benefield with Glapthorn; originally a Chapel of Ease to Cotterstock.