Horncastle is a market town situated at the western edge of the Wolds, at the confluence of two small rivers, the Bain and the Waring. The site had previously been used by the Romans for a fort. The town was the administrative centre of the Soke of Horncastle, the Horncastle Poor Law Union (1837-1930) and the Horncastle Rural District Council (1894-1974).

The earliest market and fair charter was granted to the Bishop of Carlisle in 1231, although it is clear that Horncastle was already a commercial centre. Later grants and confirmations extended the markets and fairs. By the nineteenth century the August Horse Fair was a major event. A large number of inns, public houses and beerhouses served the needs of market-goers. Shops and public facilities such as schools, chapels, and the Dispensary completed the townscape.

The town benefitted from good transport connections. Turnpike road connecting Horncastle with Lincoln was opened in 1759, and a link with Louth was completed in 1770. The Horncastle Navigation, connecting the town with the River Witham was opened in 1802, and the branch railway from Kirkstead arrived in 1855, although both are now closed.

The open fields of the parish were enclosed by an Award dated 1851, although the processs began with the enclosure Act of 1803. Proprietors of land in the parish also had ancient common rights in Wildmore Fen, which were substituted in 1820 for a defined Parochial Allotment there, as a result of the Wildmore Fen enclosure Act of 1801. Although detached from the town by several miles, this Parochial Allotment remained part of the parish of Horncastle until 1880 when it became part of the new parish of Wildmore.