MATERIALS: flint with sandstone dressings, clay tiled roof with pierced and fretted ridge tiles, tower has copper covered setback spire on 'Hertfordshire spike'. PLAN: nave, north aisle, west tower and spire
West windows above 2-light, with restored C15 roll mouldings, irregular quatrefoil heads, central cusped quatrefoil, 3 centre head and dripmould
2-light louvred openings at belfry stage, C14 style with cusped trefoil heads and roundel
South porch with gabled parapeted roof, C14 style doorway with chamfer and double ogee mouldings, dripmould with undercut moulding and foliated bosses
Nave of 2 bays externally with flint buttress with stone quoins, restored C15 2-light windows with elliptical inner heads to left-hand, cusped quatrefoils on right both under flat moulded dripmould
Chancel roof runs through from nave at same height, external stonework of C13 structure renewed 1890
Single lancet window on south wall with long and short quoins, parapeted east end, with cross finial on range, long and short quoins, east window restored C13
Three 2-light windows, 2 with segmental pointed heads with C15 stonework, window at right has flat head and is more fully renewed
4 bay nave with deep reveals to C15 windows in south wall
Tall C15 tower arch with attached octagonal columns with moulded base, caps and elliptical arch, moulded outer surround
North aisle of 4 bays, cavetto mouldings around window openings restored C15
C13 chancel of 4 irregular bays, restored and altered 1890. south wall has large arched opening to organ chamber and vestry, south window in wide chamfered reveal, with moulded clunch inner head with undercut ogee roll and chamfers
East window C13, triple lancets with engaged colonnettes between with undercut bell caps, bases with undercut roll ogee moulding, north wall with single lancet in wide chamfered reveal
Reredos of red and pink veined marble, central arched niche for cross, 3 niches either side with colonnettes and ogee trefoil heads, elaborate fretted pierced and carved top
Below south window is piscina, 2-light surround C19 in C13 style with heavily undercut mouldings but incorporating medieval heads in dripmould
Pulpit in nave, green and pink alabaster, elaborate Gothic frontal with ogee heads and shields
Pews have bench ends in Rococo style, carved in 1893 by Joseph Mayr of Oberammergau
fruit swags, rope, shell and scroll motifs, carved panelled frontals with moulded surrounds, the craftsman's name recorded on a plaque on the first pew
Principal memorial to Francis Thomas de Grey Cowper (d.1905), life size recumbent effigy with shield at feet on a panelled Italianate style tomb with carvings, mouldings and shields, by Henry Poole 1909
On east wall monument to William, second Earl Cowper (d.1764), white, black, pink and yellow veined marble, break front black marble base with panels with carved swags of fruit and flowers, moulded cornice, life sized angel pointing to a weeping putto who holds an elliptical shield with a relief head and shoulders portrait of the deceased earl
The angel's left-hand points to a cluster of putti heads surrounding a sunburst high up on the pink marble obelisk
Spencer Cowper d.1727, judge of the pleas, memorial in window embrasure on north wall, black marble cartouche with inscription, above a scrolled and pedimented surround in black marble, with a relief of Cowper in judge's robes, seated between the figures of Wisdom and Justice, made 1752 by Roubiliac
Nave: S wall above pulpit, Renaissance style marble armorial plaque, painted in polychrome, to Sir Christopher Vernon of Haddon, Derbyshire, official of the exchequer
Sir Gore Ousley (1770-1844), Ambassador to Shah of Persia, black marble surround, white monument with Persian urns and ornament
Tower: On south side altar tomb of Sir William (d.1637) and Lady Harrington and their daughter, black marble slab with 2 recumbent marble figures, with an effigy of their daughter kneeling in prayer, attributed to Epiphamious of Evesham
The most important monuments are separately listed (qv). (Victoria History of the Counties of England: Hertfordshire: London: 1902-1912: 467-8
Royal Commission on Historical Monuments (England): An Inventory of the Historical Monuments of Hertfordshire: London: 1910-: 114