St John the Baptist's Church is a closed, redundant Anglican church, partly in ruins, in what has thus reverted to the hamlet of Mongewell, Oxfordshire, England. It is recorded in the National Heritage List for England as a designated Grade II listed building, and is under the care of the Churches Conservation Trust. The ruins stand on the east bank of the River Thames, next to the former Carmel College, to the north of Mongewell Park, 2.5 miles (4 km) south of Wallingford, and near The Ridgeway long-distance path. Local Anglicans are in the parish of North Stoke: St Mary the Virgin.