St John's has a clerestoreyed nave with four-bay aisles. The arcades are early 14thc., and some of the S aisle windows date from the same time. Those in the N aisle are 19thc. replacements. The nave doorways are both of c.1300, but the S doorway has had a Tudor four-centred arch inserted and is under a 13thc. porch, while the N is unprotected. The chancel arch is of c.1300, but the chancel itself is Perpendicular with an east window of five lights. The W tower dates from the end of the 12thc., and the broach spire from the early 14thc. Romanesque features here described are the late 12thc. tower arch and bell-openings, and a fragment of an arcaded font bowl.

Harringworth was held by Countess Judith in 1086. No church was recorded.

Benefice of Bulwick and Blatherwycke with Harringworth and Laxton.

The tower arch dates from c.1180-1200, and the bell-openings are presumably a few years later than the arch. Interestingly the same kind of fictive capitals appear on the font fragment, which suggests a similar date. This kind of thing is not uncommon in north Northamptonshire. Something very similar appears in the nave arcades at Warmington.