[6] The flints, sourced from hills to the north of the town,[7] were knapped to produce smooth faces,[8] and set into lime mortar.

[7] The tower also contains Hertfordshire puddingstone, brownish-white quartzite and speckled black and white volcanic rock.

Stevenage had as its rector at this time the Reverend Thomas Alleyne,[4] who was respected and loved by his parishioners, who saw him as a father figure.

[14] During the English Civil War, the church suffered the loss of stained glass windows, murals were whitewashed and ornaments were destroyed by Roundhead supporters.

[20] Those concerned with the new town realised that new centres for people to meet were needed to create a sense of community, so several new churches were to be built.

[24] Notable incumbents who left their mark on the town include Stephen Hellard, who bequeathed a set of almshouses to the town, rent-free, provided the residents commended his soul to God every day,[10] and Thomas Alleyne, who left funds in his will for a free grammar school, which, combined with that of a yeoman, Edward Wilshire, provided The Thomas Alleyne School in 1558, surviving today as The Thomas Alleyne Academy.

Two concealed windows were discovered in the chancel with the mullions and tracery nearly perfect, as were the remains of three sedilia and a double piscina.

[35] In 1914, the rector, Canon Molony, set about to restore the church where "the rain has been streaming down the inside walls in the south-west corner of the transept and the boarding of the nave has required further temporary repairs in order to save people from going through the flooring.

[37] The church also contains six 14th- or 15th-century oak misericords, including one with a carved image of a woman with a branks in her mouth (though sometimes interpreted as a Green Man) and another of an angel.

St Nicholas' Church underwent redecoration in 2009,[40] and the parish room was refurbished in the 2010s with a kitchen and two upstairs toilets.

[6] St Nicholas' Church has been called "unremarkable" within the county of Hertfordshire in that it has fewer medieval monuments and memorials than other parishes.

It contains six visible surviving monuments from the Middle Ages,[41] five of them were brasses set into stone slabs.

[42] The only surviving brass is a memorial to Stephen Hellard, who was rector of Stevenage from 1472 until his death in 1506, and is buried in the church.

It was inscribed while Hellard was alive with a space left for his death date, but the inscription was not completed.

[44] The sixth is a late-13th century stone effigy of a lady with hands raised in prayer at the east end of the north aisle.

The colours were preserved but have since faded, and the carving has worn, but a drawing of it was made upon its discovery, showing how it looked at the time.

[45] There is no evidence as to the lady's identity, and it is not known whether the effigy would have originally been set on top of a tomb or within a wall.

It was carved in Watts Cliff Stone, a Millstone Grit rich in plagioclase which gives it a lilac colour, from a quarry near Elton, Derbyshire.

[50] St Nicholas' Church contains a "surprising" number of drawings on its pillars, giving insight into the minds of the medieval inhabitants of Stevenage.

They are in the form of masons' marks, geometric designs, human figures, shields, crosses and writing.

[53] The lychgate at the entrance to the churchyard was erected in 1895, after Mrs George Smyth left money in her will devoted to the expense of doing so.

[56] The churchyard is in a conservation area[53] and plays an important part in the countryside by acting as a refuge for birds, mammals, insects and plants including goldilocks buttercup, meadow saxifrage and lady's smock.

[57] Other trees planted in the churchyard include large-leaved lime, Swedish whitebeam, Norway maple, copper beech, English oak, hornbeam, false acacia, Indian bean, Turkey oak, ornamental crab, white cherry and mountain ash, many of which were planted in memory of various people.

[58] The churchyard is maintained by the church from bequests and contributions from the parishioners and Stevenage Borough Council.