Parish Church. Mid C15, with early C13 north arcade and C14 chancel arch and other fragments. Chancel and south chapel paid for by Sir John Markham, 1468. Restored 1897. Chancel, south chapel with stair turret, north chapel, nave with aisles, north and south porches, west tower. Coursed squared ironstone with dressings and east end of Ancaster stone ashlar. Lead roofs. Perpendicular style. Moulded plinth and coped parapets throughout. Windows have mainly deeply pointed arches and hood moulds with stops. Chancel, 3 bays, has crenellated parapet, and diagonal buttresses to east. 5-light segmental pointed east window with traceried transom and panel tracery. South side has a pointed arched 2-light window also with traceried transom. North side has three linked 2-light windows, set high above a former vestry, now demolished. Below them, a segment headed doorway and to its left, and ogee piscina. South chapel has diagonal buttresses and 3 linked 2-light windows with cusped lights. East end has a segmental pointed 3-light window with panel tracery. At the south west corner, a crenellated octagonal turret, 2 stages, with a staircase and a sanctus bell. Single bay north chapel has a coped east end with a segmental pointed 3-light window with ogee heads and cusped tracery. On the north side, a similar window with plain panel tracery. South aisle has four 2-light windows with cusped heads, and at the west end, a diagonal buttress and a similar window. North aisle has a buttress to east and a diagonal buttress to west. 4 windows identical to the south aisle, one of them raised above the porch. Parapeted south porch has moulded doorway with single shafts and hood mould, flanked by diagonal buttresses. INTERIOR has moulded doorway with hood mould, boarded ceiling with spine beam, and stone benches. Unbuttressed, unparapeted north porch has a similar doorway, flanked to right by a cusped stoup. INTERIOR similar to south porch. Square west tower, 3 stages, has clasping buttresses to the lower stages and angle buttresses above, chamfered string courses, crenellated parapet and gargoyles. To west, a Tudor arched doorway with hood mould, mask stops and shields in the spandrels. Above it, a 3-light window with cusped heads and panel tracery under a stepped hood mould. North side has blank lower stages. South side has a clock, 1919, on the middle stage. Bell stage has on each side two 2-light cusped bell openings under an ogee gable with crest. INTERIOR rendered, with largely original low pitched roofs with wooden brackets. Chancel has a C14 moulded arch with mutilated hood mould and clustered shaft responds, and a restored perpendicular wooden screen. The east window is flanked by mutilated canopied niches in the angles. The south side has an elaborate cusped piscina and aumbry, and a buttressed and vaulted sedilia with pendant gables. 2 bay arcade to south chapel, with moulded arches and central quatrefoil pier. The east bay has brackets to east and west, on ornate angel corbels. North side has to east a Tudor arched roll moulded doorway and a small ogee piscina. To west, an opening to the north chapel similar to the chancel arch. South chapel east window has flanking canopied niches in the angles. South side has to east an aumbry and enriched piscina, and to west, another piscina. West end has a stone screen with door and an unglazed 2-light window, with a wooden rood loft above. North chapel, now organ chamber, has a restored perpendicular screen with rood loft above. Small piscina in south east corner. Nave has early C13 north arcade, 3 bays, with double chamfered round arches, linked hood mould and round piers. C15 south arcade has moulded pointed arches with hood moulds, and octagonal piers. At the west end, tall moulded tower arch with round responds and C20 screen. South aisle has to east a moulded pointed arched doorway to the stair turret, and an altered, moulded west door, both with hood moulds. North aisle has regular fenestration. Both aisles have restored lean-to roofs. Fittings include octagonal C11 scalloped font, restored traceried panelled oak pulpit dated 1634, on C19 stone base, and several benches and stalls, C14 and C15, with unusual poppyheads and candle holders. Marble benefactions tablet, 1717. Memorials include a small incised slab, 1494, to Dorothy Markham. (The Buildings of England: Pevsner N, Harris J & Antram N: Lincolnshire: London: 1964-1989: 638-639; Austin F: St Lawrence Church, Sedgebrook; a short history: Sedgebrook: 1980-1990).