The Earls of Sefton held the subsidiary titles Viscount Molyneux, of Maryborough (modern day Portlaoise) in the Queen's County (created 1628), in the Peerage of Ireland, and (from the 2nd Earl onwards) Baron Sefton, of Croxteth in the County Palatine of Lancaster (created 1831), in the Peerage of the United Kingdom.

It was bequeathed to the City of Liverpool by the 7th and last Earl of Sefton and his wife, the former Josephine Gwynne Armstrong (1903–1980), who was the final member of the Molyneux family to live at Croxteth.

The American-born Countess of Sefton, nicknamed "Foxy" and formerly a fashion model of great beauty, was a lifelong friend of the Duchess of Windsor.

They can be shown to have held a large moated manor and St. Helen's Church at Sefton without interruption from about 1100 to 1700 before they moved to Croxteth Hall.

Scribes and monks in the Middle Ages spelt names as they sounded, so it is common to find several variations that refer to a single person.

The variations of the name include Molyneaux, Molinex, Mullinix, Mullenneix, Mullineaux, Molinieux, Molinaux, Molineaux, Mollineaux, Molineux, and several others.

Although Anglo-Norman surnames like Molyneaux are characterized by many spelling variations, the form Molyneux has prevailed with the modern trend towards standardisation.