St Mary Moorfields is a Roman Catholic church in Eldon Street near Moorgate, on a site previously known as Moorfields. It is the only Catholic church in the City of London. Prior to a 1994 boundary change, the church was in the Borough of Hackney, such that there were no Catholic churches in the City.

Moorfields was an open space, partly in the City of London, lying adjacent to – and outside – its northern wall, near the eponymous Moorgate. It was known for its marshy conditions, the result of the defensive wall acting as a dam, impeding the flow of the River Walbrook and its tributaries.