West tower and north aisle are probably late C15.
Rood stair turret to north wall remodelled as a doorway probably in the C17.
3-stage C15 embattled
pinnacled west tower is complete and unaltered: 4-centred moulded west doorway with square hoodmould and flat relieving arch circa C17-C18 2- panel door, 3 light repaired Perpendicular window with coloured glass, over
North aisle has C15 granite Perpendicular windows, arched window at either end and sqaure headed to north wall, all with cinquefoil headed lights and all with hood moulds.
The 3-light east window also with tracery and coloured glass.
Chancel has 3-light Perpendicular east window with tracery and coloured glass.
South wall with 2 C19 buttresses has single light window between buttress with old jamb to one side and resited arch stone over, possibly a remodelling of an original C13 window.
The south transept probably remodelled in the C15 and partly rebuilt in the C19 has C19 3 light traceried granite window in early Perpendicular style to the south gable end.
The porch outer doorway has rubble jambs carrying a 2-centred chamfered freestone arch possibly C13 or resited.
The C15 moulded inner doorway is 4-centred almost basket arched.
Niche in north wall of chancel may be in original C13 window position.
Monuments: one to the west wall of the south transept to Humphry Millet Grylls of Bosahan, died 1834 aged 44.
Sited near the mouth of the beautiful Gillan Creek almost on the shoreline, this church has survived less altered than most since the C15 and the waggon roofs are particularly remarkable.