St. Mary of the Immaculate Conception is a historic Roman Catholic church located at 6th and Pine Streets in Wilmington, New Castle County, Delaware. It was built in 1858 and is a brick church building trimmed in limestone and measuring about 100 feet long and 60 feet wide. The front facade features three brick towers; two corner ones are set diagonally, with onion-shaped domes topped with crosses and the center square tower (built 1881), now used as a belfry, has arched louvred openings. The dome on the center tower replaced an original wooden belfry and smaller dome destroyed by fire in March 1966. A parochial Catholic school, St. Mary's, was built on the adjacent property in 1866. St. Mary's is the only church in Delaware associated with Saint John Neumann, Bishop of Philadelphia 1852-1