The tower is supported by four arches on clustered shafts, and the nave is divided from its aisle by four arches on each side. The east wall of the chancel is modern. Three sedilia of the Decorated period occupy the usual position in the chancel. In one of the windows on the east side of the south transept occurs the only instance of the dog-tooth ornament in the interior of the church, and there is a piscina in both of the side walls of the same transept. Darlington is the only church in the county which retains a rood-loft. On the south of the chancel is the vestry, which has been greatly modernized. The only monumental effigy is that of an unknown lady with a book in her hand. It dates from the early thirteenth century, and is placed at the west end of the nave. After the two churches last mentioned, the church at Sedgefield, dedicated to St. Edmund the Bishop, but formerly dedicated to the Virgin, is probably the finest in the county. The nave and chancel date from the Early English period. The tower is very fine, of Perpendicular date and of three stages, crowned by battlemented parapets and small spirelets standing on angle buttresses. The Rev. J. F. Hodgson is of the opinion that it was intended to crown the tower with an open lantern, as at St. Nicholas’ Cathedral, Newcastle. There are two transepts; the south contains the chapel of St. Thomas, and in its east wall are two piscinas, one of which is trefoil-headed; and in the south wall are two pointed recesses occupied by much mutilated male and female effigies, the latter dating from the later fourteenth century. The north transept contains the Chapel of St. Katherine, and is now known as the Hardwick porch. Two of its ancient windows still remain, and fix its date as 1328. The east window is filled with Late Decorated tracery. The nave is divided from the aisles by three pointed arches, supported by clustered pillars on moulded bases. The capitals are richly carved and very interesting. The font is octagonal and of Frosterley marble, dating from the end of the fifteenth century, and charged on each side with armorial shields, most likely carved in the seventeenth century. The stall work of the chancel is ascribed to the latter part of the seventeenth century, and the rich chancel screen to a slightly earlier date. On the north side of the chancel is the grave cover of Andrew de Stanley, first master of Greatham Hospital. Two interesting brasses of skeletons in shrouds are preserved in the vestry, and were originally inlaid in one slab. Another small brass is in the south transept. It is considered to be one of the earliest in England, and represents a lady in loose robe with tight sleeves and wimple and hood. There is another brass to the memory of William Hoton, engraved with a helmet and crest of three trefoils. Of the five bells, one is of pre-Reformation date, bearing the inscription "✠ TRINITATE SACRA FIAT HEC CAMPANA BEATA," and the arms of Rhodes and Thornton.