Great Gaddesden is a village and civil parish in the Dacorum District of Hertfordshire, England. It is located in the Chiltern Hills, north of Hemel Hempstead. The parish has borders with the parishes of Flamstead, Hemel Hempstead, Nettleden and Little Gaddesden and also to Studham in Bedfordshire.
The Church of St. John the Baptist was probably the site of a pre-Christian sanctuary. The church shows features of every period since the 12th century. Part of the chancel with Roman bricks dates back to the early 12th century. The old church was extended by the south aisle in the 13th century and the north aisle in the 14th century, the west tower was built in the 15th century and the north chapel in the 18th.
Gaddesden Place, positioned east of the small village, was built from 1768 to 1773 for the Halsey family. It is surrounded by a huge park. In 1905 a fire destroyed the interior of the main house.
The River Gade has its name from Gaddesden. Its clear water is used for watercress beds along the river and at Water End south of Great Gaddesden village is an old corn mill powered by the stream. The bridge over the river at Water End has a medieval appearance but was built in the 19th century.