The oldest parts of the Church of England parish church of Saint John the Baptist are the nave and the arcade of the north aisle, both of which were built late in the 12th century. They are in the transitional style between Norman and Early English. In the 13th century the nave and north aisle were extended westwards by the addition of a fourth bay. In the 14th century a clerestory and a two-bay south aisle were added to the nave and most of the doors and windows were remodelled. Also in the 14th century the interior was decorated with wall paintings including a Pietà, a Saint George and a Doom. The bell tower was built around 1400 and the present Perpendicular Gothic east window of the chancel was added in the 15th century. Many of the wall paintings were painted over with limewash after the English Civil War.
The tower has a ring of five bells, all cast by Henry III Bagley of Chacombe in 1741. They are currently unringable because the fourth bell is cracked.
St. John's is now one of eight ecclesiastical parishes in the Ironstone Benefice.
Non-conformist groups in Hornton included Baptists in the 17th century and Quakers in the 17th and 18th centuries. Hornton had a Primitive Methodist congregation by 1836, which had built its own chapel by 1842. Hornton's present Methodist church was built in 1884.