Laid out between 1824 and 1827, the square is part of the New River Estate and named after Sir Hugh Myddelton, who was responsible for building the New River in the early 17th century. The square and St Mark's Church (1827) were designed by William Chadwell Mylne, surveyor to the New River Company from 1811. The church was gutted and the north side of the square destroyed in the 1940s, as a result of WW2 bombing, and rebuilt in replica by the New River Company. The gardens contain many mature trees, seating and raised rose beds. There is a children's playground beside the church.