This surname was of the baptismal group of surnames and was derived from the Old English word ' aeoelheard '. The name was originally brought into England in the wake of the Norman Conquest of 1066. Early records of the name mention Adelardus (without surname) listed in the Domesday Book of 1086. Adam Adelard, 1273 County Cambridge. John Adelard was documented in 1327 in County Yorkshire, and Richard William Adlard was listed in the Yorkshire Poll Tax of 1379. ADELARD (without surname) was a 12th century philosopher. He studied at Tours, and travelled widely in Italy and the near east, and is attested at Bath in 1130. His philosophical and scientific writings include many important translations from the Arabic into Latin. Adelard Baat was recorded as the chaplain of Magdalen, Oxford University in the year 1505. William Tollitt married Elizabeth Adlard at St. George's, Hanover Square, London in the year 1794. When the coast of England was invaded by William The Conqueror in the year 1066, the Normans brought with them a store of French personal names, which soon, more or less, entirely replaced the traditional more varied Old English personal names, at least among the upper and middle classes. A century of so later, given names of the principal saints of the Christian church began to be used. It is from these two types of given name that the majority of the English patronymic surnames are derived and used to this day.

The associated arms are recorded in Sir Bernard Burkes General Armory. Ulster King of Arms in 1884.