Mongewell (first syllable rhymes with sponge) is a village in the civil parish of Crowmarsh, about 1 mile (1.6 km) south of Wallingford in Oxfordshire. 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.
Grim's Ditch to its north has its main section north of the village, a Scheduled Ancient Monument. In order to provide a level climb up to the first major hill of the long Chiltern Hills range to the east and northeast this has embankments and cuttings, with thousands of tonnes of earth displaced in the Bronze Age in order to facilitate access by foot.
The ecclesiastical parish was joined by a civil parish in the 19th century, but in 1932 was split, mostly joining a new civil parish naned Crowmarsh, but a small part was added to Rotherfield Greys parish.
Given the location next to the Ridgeway and containing a spring well, the name could be derived from the old English word Mangere as in fish monger, iron monger, war monger etc. meaning a dealer in a specific commodity. So it would be the traders well. 
Replacing the original Georgian Mongewell House of Barrington, a large brick mansion in William and Mary style was built in 1890 for Alexander Frazer whose initials can be seen on the lodge gates (Pedgley and Pedgley, 1990). After Fraser died in 1916, the house became a hospital for wounded officers in World War I. In 1918, it was sold to the American millionaire Howard Gould. Because he was an atheist, he had the lane to the now ruined Mongewell church sunk so that he would not see the parishioners attending service. He sold the house in 1939 and the Royal Air Force occupied it until 1945. In 1942 it became the Headquarters for No 2 Group RAF of Bomber Command led by Air Vice Marshal Basil Embry. On the Staff there for six months before his capture as a POW was the World War II night fighter ace, Wing Commander Bob Braham (Braham, 1984).
At the end of the war the house was once more used as a hospital before becoming derelict. A Jewish boarding school, Carmel College occupied Mongewell Park from 1948 to 1997, this added several architecturally listed buildings, including its synagogue and the Julius Gottlieb Gallery and Boathouse, at a national level.
As of June 2007, it is planned to redevelop the site for housing.
- Grim's Ditch - section from the south of Mongewell Park Lodge to the south of Nuffield Church English Heritage. "Details from listed building database (1006368)". National Heritage List for England.
- L. F. Salzman (editor) (1939). "The Domesday survey: The text". A history of the County of Oxford: Volume 1. Institute of Historical Research. Retrieved 20 August 2011.
- Church of St John the Baptist English Heritage. "Details from listed building database (1059580)". National Heritage List for England.
- Vision of Britain: Boundary map
- Vision of Britain website
- Word Definition
- The Gallery building English Heritage. "Details from listed building database (1379942)". National Heritage List for England.
- Braham, J.R.D. (1984) Night Fighter, Specially illustrated edition, New York : Bantam Books, p. 186–195, ISBN 0-553-24127-3
- Pedgley, B. and Pedgley, D. (1990) Crowmarsh – A history of Crowmarsh Gifford, Newnham Murren, Mongewell and North Stoke, Crowmarsh History Group, p. 50–54, ISBN 0-9516305-0-4