First found in Shropshire where they were anciently seated as Lords of the Manor. After the Battle of Hastings in 1066, William, Duke of Normandy, having prevailed over King Harold, granted most of Britain to his many victorious Barons. It was not uncommon to find a Baron, or a Bishop, with 60 or more Lordships scattered throughout the country. These he gave to his sons, nephews and other junior lines of his family and they became known as under-tenants. They adopted the Norman system of surnames which identified the under-tenant with his holdings so as to distinguish him from the senior stem of the family. After many rebellious wars between his Barons, Duke William, commissioned a census of all England to determine in 1086, settling once and for all, who held which land. He called the census the Domesday Book, indicating that those holders registered would hold the land until the end of time. Hence, conjecturally, the surname is descended from the tenant of the village and lands of Sleapa, held by William Pantulf from Earl Roger, who was recorded in the Domesday Book census of 1086.

Some of the first settlers of this family name or some of its variants were: Lancelot Sleep, who arrived in Maryland sometime between 1640 and 1648; Thomas Slape, an emigrant in bondage, who arrived in Maryland in 1738; as well as Mary Sleep, who arrived in St. John, N.B. in 1834..

For more information on the last name Sleep, the PDF Surname History is available for purchase as well as other products.