The oldest building in central Watford, dating in parts to the 12th century, though most of what stands today is 15th-century rebuilding around an earlier core. The tower is the original Norman work; the nave was widened in the perpendicular style.
The real interest is inside: the Essex Chapel on the north side holds the late-Tudor tombs of the Morrison family, who held Watford manor before the Capels (later Earls of Essex). The chapel's painted plasterwork and recumbent effigies survived the Reformation almost intact and are among the best private chapel monuments in Hertfordshire.