Aylesbury is an ancient settlement in the centre of Buckinghamshire. An Iron Age hill fort was excavated in the town centre in the 1990s, and the town lies on Akeman Street, the Roman road from Bicester. In the Anglo-Saxon period it was already an important market town, although the county town was then Buckingham, in the NW of the county. Aylesbury superseded Buckingham as the county town in 1529, following a declaration by Henry VIII. According to rumour Henry was trying to please Thomas Boleyn, who held the manor and whose daughter, Anne, the king wished to marry, but Aylesbury was also growing quickly at that time, and was more centrally sited than Buckingham.

The Vale of Aylesbury runs from W to E through the town, and is a continuation of the Vale of the White Horse, largely in neighbouring Berkshire. It is a lowland, agricultural region on a clay substrate, supporting mixed farming and especially dairy cattle. The surrounding landscape is generally wooded with hedges. Aylesbury was always a market town rather than a manufacturing one, although flour was ground there for the surrounding parishes from the later middle ages until the 20thc. Aylesbury is now a dormitory town for London commuters, with a fast service to Marylebone. Large areas of its historic centre were demolished in the 1950s and '60s, and housing estates were built around the centre. St Mary's is in the town centre, and the neighbouring streets, e.g. Parson's Fee, contain attractive timber-framed houses, but the inner ring road presses very close on the historic centre. St Mary's is a large cruciform church with a crossing tower. The nave has six-bay aisles with late-13thc. arcades. The E end of the N aisle was widened in the 14thc. The chancel is basically 13thc., but the E and S walls were rebuilt in the 19thc., and the present E window is a 19thc. replacement for a five-light Perpendicular window that is now in the grounds of Greenend House, Rickford's Hill. The transepts and crossing also retain some 13thc. ornament, but this area too was heavily restored in the 19thc. A 14thc. Lady Chapel was added to the E side of the S transept, and is now divided into a vestry and the Chapel of St Luke. On the N the corresponding site is occupied by the parish office. The tower is 13thc. with a plain parapet (although early views show battlements), and behind this is a square, lead-covered clock stage with a lead spike. Pevsner suggests that the upper parts are a 19thc. copy of a 17thc. timber spire. There was a major remodelling in the 15thc., when a clerestorey was added to the nave and many windows were replaced, but as Pevsner notes, the overall impression is of the 19thc. In 1840 Sir George Gilbert Scott found it in a dilapidated state, and he restored it progressively in campaigns of 1849-55 (rebuilding of nave and crossing piers, removal of galleries, repair of nave and aisle roofs), and 1866-69 (replacement of E window, rebuilding of upper parts of tower, renewal of exterior stonework). More recently the W end of the nave has been remodelled as a café (the refectory) and kitchen, with a stage erected in the three westernmost bays for the tables, the servery in the S aisle and porch, the kitchen in the N aisle and the lavatories to the W, under a modern gallery.

The only Romanesque feature is the font, an important example of the Aylesbury type, which is now in the centre of the refectory at the W end of the nave; its base partly concealed below the staging.

Early traditions connect Aylesbury with Edith, the daughter of Penda of Mercia (d.655) and aunt of St Osyth. It came to the crown in the person of king Edwig, and was the site of a mint in the reigns of the latest Anglo-Saxon kings. Edward the Confessor was lord of Aylesbury, and it remained a possession of the crown until 1204, when king John granted the town to Geoffrey fitz Piers, earl of Essex. It remained in this family until John Fitz Piers threw in his lot with Simon de Montfort at Evesham, when it was seized by the crown and given to Gilbert de Clare. It was returned to the Fitz Piers in 1267–68. The male line failed in 1297 with the death of Richard Lord Fitz John, and Aylesbury eventually passed to the heirs of his sister, Joan Butler, and into the possession of James Butler, Earl of Ormonde. The Ormondes were dispossessed during the Wars of the Roses, but regained the town in 1485, when Thomas, the 7th earl came into possession. He was succeeded by his daughter, Margaret, married to Sir William Boleyn. In 1538 Margaret and her son Thomas sold it to Sir John Baldwin who, as Chief Justice of Common Pleas, had presided over the trial of Thomas's daughter Anne Boleyn two years before. The parish is now in the benefice of Aylesbury (St Mary) with Bierton and Hulcott.

The font belongs to a group of 22 (according to Pevsner) centred on Aylesbury, of which thirteen (not all complete) are in Buckinghamshire. These are at Aylesbury, Bledlow, Buckland, Chearsley, Chenies, Great Kimble, Great Missenden, Linslade, Little Missenden, Monks Risborough, Pitstone, Weston Turville and Wing. Of these the finest are at Aylesbury, Chenies, Great Kimble, Great Missenden (base only), Weston Turville and Wing (base only). Others in the group have shallower or less complex carving, while a further three in the county, at Ludgershall, Saunderton and Haddenham, are less adept copies of the design. Outside Buckinghamshire there are related fonts at Duston and Eydon in Northants, and at Barton-le-Clay, Dunstable, Flitwick and Houghton Regis in Bedfordshire. These fonts are normally dated late in the 12thc., c.1170-90. Thurlby suggests, on the basis of comparisons of foliage forms on the Aylesbury and Weston Turville fonts with sculpture at St Alban's Abbey dating from the abbacy of Simon (1167-83), and on the resemblance between these fonts and liturgical chalices, that the sculptors were copying St Albans metalwork, perhaps of the kind produced by one Master Baldwin according to an account by Matthew Paris. Of the other fonts in the group, the Weston Turville font is perhaps closest to the Aylesbury font. The two have similar rim decorations and both have fluted bowls, although the Aylesbury bowl has a double-curved (cyma) profile. The motifs on the shields of the base are similar too, although the Weston Turville base is single scalloped. The nested chevron central roll of the Aylesbury font is also more complex, having two units of chevron where Weston Turville has only one.