Mellor stands in the High Peak on the border with Derbyshire. Indeed it was in Derbyshire until 1936 when it was reassigned, along with neighbouring Ludworth, to Cheshire. Recent excavations have disclosed an Iron Age hill fort alongside the church. St Thomas's was formerly a chapel of ease to Glossop in Derbyshire, and remains in the Glossop Deanery of the Diocese of Derby. The church has a 15thc. W tower, but whatever was to the east of this was replaced from 1815 to 1830 with a simple aisleless nave and chancel of brick. Something similar took place at Church Lawton. The only Romanesque feature is the font, one of the most interesting in the county.