The area which would become the parish of St Thomas the Apostle was anciently part of the parish of
St Stephen, which covered the town of Launceston and extensive surrounding areas. Several
chapels of ease were established to serve the town, particularly in light of the parish church at St Stephen's being peripheral to the main urban area after the focus for the town shifted southwards.
Launceston Priory stood just south of the
River Kensey, in between the original centre of Launceston around St Stephen's to the north and the newer centre (historically also known as Dunheved) which grew up around
the castle to the south. The area south of the Kensey became the parish of
Launceston St Mary Magdalene after that former chapel of ease was rebuilt in the early 16th century. Launceston Priory was
dissolved in 1539. The former priory church, dedicated to
Thomas the Apostle, was retained to serve as another chapel of ease. It was subsequently made a parish church in 1726 and given a parish covering an area south of the Kensey and north of the castle and town centre, and also extending into rural areas to the west of the town. Part of the parish of St Thomas the Apostle was within the borough boundaries of Launceston from the creation of the parish in 1726. The area within the borough was known as the
hamlet of St Thomas Street. Parish functions under the
poor laws were administered separately for St Thomas Street and the rest of the parish, and so St Thomas Street became a separate civil parish in 1866 when the legal definition of 'parish' was changed to be the areas used for administering the poor laws. The
Local Government Act 1894 directed that civil parishes were no longer allowed to straddle borough boundaries, and so the parish was split along the borough boundary. The
ecclesiastical parish of St Thomas the Apostle after 1894 therefore straddled three civil parishes: "St Thomas Street" covering the part that was in the borough of Launceston prior to 1889, "St Thomas the Apostle Urban" covering the western fringes of the town that had been added to the borough in 1889, and "St Thomas the Apostle Rural" covering the areas outside the borough. The civil parishes of St Thomas Street and St Thomas the Apostle Urban were abolished in 1922 when all the
urban parishes within the borough were united into a single parish called Dunheved, otherwise Launceston. Despite the fragmentation of the civil parishes, the ecclesiastical parish remains essentially as it was on its creation in 1726, covering the part of Launceston north of the old walled town and south of the Kensey and stretching into the rural areas west of the town. ==Parish church==