The parish of St Mary Hoo lies on the north side of the Hoo peninsula, extending from the central ridge of the higher ground to a northern marshland fringe and foreshore on the River Thames. Bordered east and west by the parishes of Allhallows, and High Halstow, its chief developments are the village of St Mary Hoo, the hamlet of Fenn Street, and further ribbon development along the Ratcliff Highway, the principal routeway. Historically, its economy was largely agricultural, but like others on the peninsula, St Mary Hoo saw industrial and military development in the 19th and 20th centuries, mainly in the form of gravel extraction, explosives storage, war-time defensive structures and land fill waste disposal. St Mary's Hall was the home of the influential agriculturalist Henry Pye, the so-called 'King of the Hundreds' who progressed farming practices and played a decisive role in the creation of the 'Hundred of Hoo Railway Company'. Yet the parish was bypassed by the railway and by the upgrading of the peninsula's main road, the A228. As a result, St Mary Hoo retains a strongly agricultural character, and its landscape is one of fields, orchards and marshland pasture with dispersed residential clusters and isolated farmsteads.