Mongewell is a village in the civil parish of Crowmarsh in the South Oxfordshire district, in Oxfordshire, England, about 1 mile (1.6 km) south of Wallingford. Mongewell is on the east bank of the Thames, linked with the west bank at Winterbrook by Winterbrook Bridge. The earthwork Grim's Ditch, now part of The Ridgeway long-distance footpath, passes through the northern part of it and is a scheduled ancient monument. It has a church called St John the Baptist's Church.