Watford is a borough in the south of Hertfordshire, 15 miles NW of central London. It developed on the River Colne and was granted a market, perhaps as early as Henry I's reign. It was certainly in existence by the time of Henry II. St Mary's on the High Street is a large church, mainly of the 15thc. It consists of a broad W tower with a Hertfordshire spike; a nave with 6-bay aisles and clerestoreys, and a chancel with N and S chapels. The earliest fabric is 13thc, foung in the chancel arch and the piscina. The S nave arcade is of the same period but the N arcade, although very similar, dates from the 15thc, as do the clerestorey windows and the outer aisle walls. The S chapel was rebuilt by William Heydon 1505, while the N or Morison Chapel dates from 1595-96. It contains magnificent tombs by Nicolas Stone of Sir Charles Morison (d.1599) and his son, also Charles (d.1628). In a corner of the Morison Chapel are the remains of a Romanesque font and other loose stones including a 12thc. voussoir and a nook-shaft section. These are recorded below. The church was restored in 1848 and again by John Thiomas Christopher in 1871. In 1979 a large octagonal church hall was built on the S side of the church.

Watford is not named in the Domesday Survey, but might be included with Cassio. It certainly belonged to St Albans Abbey from an early date; perhaps given by Offa, King of Mercia (d.796) as part of his gift of Cassio, or possibly via a gift of Ethelgifu (see VCH, 451). It remained in the possession of the abbey until the Dissolution, when it passed to the Crown.

The font was discovered in pieces during the restoration of the church in the 1870s. At that time the font in use dated from 1701. A new font was carved in 1871; the 1701 font given to St John's, Sutton Road (where it remains) and the Norman pieces reassembled and given to St James, Watford Fields. This church closed in 1972 and the building passed to the school next door for use as a sports hall. The Norman font was returned to St Mary's. Victoria County History (v.2, 464) recorded 'some pieces of twelfth-century masonry found during repairs... in a vestry at the W end of the N aisle'. These may be those now in the N chapel.

The voussoir is either a jambstone or from a very large arch decorated with lozenge ornament on face, soffit and angle. The lozenge decoration is elaborate and the effect must have been quite spectacular. Lozenge ornament is not common locally, although Hemel Hempstead W doorway has a fine example. The spiral decorated nook-shaft is again high-quality work, and both should be dated to the 1150s or '60s.