The Anglican parish church, St Denys', fronts onto the market place; the oldest parts date to the late-12th century and the broach-spire, built around 1220, is one of the oldest in England.

Non-conformist meetings took place on Hen Lane (later Jermyn Street) from about 1776.
The Congregationalists who met there constructed a chapel on Southgate in 1867–68 (extended in 2007); in 1972, it became Sleaford United Reformed Church, which merged with Sleaford Community Church to form Riverside Church in 2008.
Wesleyans first met in the 1790s at the house of Thomas Fawcett on Westgate.
They built a chapel nearby in 1802, which was replaced in 1823; it housed the congregation until 1848 when a larger one was built on North Street.
It was demolished and replaced by another on the same site in 1972.
A Baptist chapel was built in Old Sleaford in 1811 to house a congregation of 250, it served the Strict Baptists until possibly the mid-20th century.
The premises have been converted into a house.
A Wesleyan Reform Methodist chapel opened in West Banks in 1864, but since 1896 has been occupied by the Salvation Army.

The Fens were increasingly cultivated after the Napoleonic Wars, prompting migrant Catholic Irish farm-workers to move to the area.
By 1879 a Roman Catholic missionary, Father Hermann Sabela, was conducting services in the town.
A Catholic school and chapel were built in 1881 on land in Jermyn Street and in 1888, Our Lady of Good Counsel Roman Catholic Church, opened beside it.
The incumbent priest is Father Michael John Bell, who was appointed in 2001.
Mass is held on Sundays and throughout the week.

The Sleaford Muslim Community Association has met in St Deny's Church Hall since the early 2000s.
A prayer hall was opened on Station Road in 2015.
Protests were planned by the English Defence League, but were cancelled.

Sleaford Spiritualist Church opened in about 1956 on Westgate.
The Anglican parish church, St Denys', fronts onto the market place; the oldest parts date to the late-12th century and the broach-spire, built around 1220, is one of the oldest in England.
Non-conformist meetings took place on Hen Lane (later Jermyn Street) from about 1776. The Congregationalists who met there constructed a chapel on Southgate in 1867–68 (extended in 2007); in 1972, it became Sleaford United Reformed Church, which merged with Sleaford Community Church to form Riverside Church in 2008. Wesleyans first met in the 1790s at the house of Thomas Fawcett on Westgate. They built a chapel nearby in 1802, which was replaced in 1823; it housed the congregation until 1848 when a larger one was built on North Street. It was demolished and replaced by another on the same site in 1972. A Baptist chapel was built in Old Sleaford in 1811 to house a congregation of 250, it served the Strict Baptists until possibly the mid-20th century. The premises have been converted into a house. A Wesleyan Reform Methodist chapel opened in West Banks in 1864, but since 1896 has been occupied by the Salvation Army.
The Fens were increasingly cultivated after the Napoleonic Wars, prompting migrant Catholic Irish farm-workers to move to the area. By 1879 a Roman Catholic missionary, Father Hermann Sabela, was conducting services in the town. A Catholic school and chapel were built in 1881 on land in Jermyn Street and in 1888, Our Lady of Good Counsel Roman Catholic Church, opened beside it. The incumbent priest is Father Michael John Bell, who was appointed in 2001. Mass is held on Sundays and throughout the week.
The Sleaford Muslim Community Association has met in St Deny's Church Hall since the early 2000s. A prayer hall was opened on Station Road in 2015. Protests were planned by the English Defence League, but were cancelled.
Sleaford Spiritualist Church opened in about 1956 on Westgate.
Sleaford