This is a very interesting surname is English, although its ultimate origin may lie across the sea possibly in France. It is well recorded in the surviving church registers of the city of London from at least the end of the Elizabethan era, and is presumably locational. We say presumably because a search of the gazetters for the past two centuries has not revealed where this place is or was. 'Lost' medieval villages and even small towns are a feature of the British Isles, and it is estimated that at least three thousand surnames do originate from former sites, whose only public reminder is usually the surname itself. In this case though one would expect to be able to identify the site. The dictionaries do record various places commencing with Mount such as Mountainacre, Mountford, Mountjoy, Mountney and others, however Mountney is in Normandy, and Mountjoy is believed to be near Jerusalem, so perhaps Mountstephen is or was outside of the British Isles. Early recordings include Richard Montstephen, a christening witnress at St Dunstans in the East, Stepney, on April 3rd 1608, and John Mountstephen who married Martha Butteriss at St Martins in the Field, Westminster, on January 13th 1801.