From the time of the Norman Conquest until the early 1900s Seagry parish was roughly triangular in shape, with the 'apex' at the bottom and a flat top bordering Somerford parish. The triangle was divided almost equally in two halves by the road from Sutton Benger to Somerford; the western half of the triangle included the village of Upper Seagry (formerly Over Seagry) and the eastern half of the triangle included Lower Seagry (formerly Nether Seagry).

The western boundary was close to the western edge of Upper Seagry, and the road to Stanton St Quintin was in Sutton Benger and Draycot Cerne parishes.

The three parishes of Draycot Cerne, Sutton Benger and Seagry became one parish, called Sutton Benger, in 1934; the parish of Seagry temporarily disappeared. However, Sutton Benger parish was split in two by the building of the M4 motorway, and all the land to the north of the motorway became the new parish of Seagry in 1971.