St Mary de Castro or St Mary in Castro ('St Mary in the Castle') may refer to:
St Mary sub Castro, Dover, England, a church in the grounds of Dover Castle Church of St Mary de Castro, Leicester, England, in the former bailey of Leicester Castle Chapel of St Mary de Castro, Chester Castle, England St Mary de Castro, Canterbury, England, demolished around 1486, now the site of the White Hart St Mildred's Church, Canterbury (Church of St. Mildred with St. Mary de Castro)