Waltheof, 1st Earl of Northampton (d. 1076) was the last of the Anglo-Saxon earls, remaining in England for a decade after the Norman conquest.

He was a son of Earl Siward of Northumbria, and, although he was probably educated for a monastic life, became earl of Huntingdon and Northumbria about 1065. After the Battle of Hastings he submitted to William the Conqueror; but when the Danes invaded the north of England in 1069 he joined them and took part in the attack on York, only, however, to make a fresh submission after their departure in 1070. Then, restored to his earldom, he married William's niece, Judith, and in 1072 was appointed Earl of Northampton.

The Domesday Book (ordered to be prepared by William the Conqueror, and finally completed in 1086) mentioned Waltheof ("Walleff"); "'In Hallam ("Halun"), one manor with its sixteen hamlets, there are twenty-nine carucates [~14 km²] to be taxed. There Earl Waltheof had an "Aula" [hall or court]. There may have been about twenty ploughs. This land Roger de Busli holds of the Countess Judith." (Hallam, or Hallamshire, is now part of the city of Sheffield, in the county of South Yorkshire).

In 1075 Waltheof joined the conspiracy against the king arranged by the earls of Norfolk and Hereford; but soon repenting of his action he confessed his guilt to Archbishop Lanfranc, and then to William, who was in Normandy. Returning to England with William he was arrested, and after being brought twice before the king's court was sentenced to death. On the 31st of May 1076 he was beheaded on St Giles's Hill, near Winchester. Weak and unreliable in character, Waltheof, like his father, is said to have been a man of immense bodily strength. Devout and charitable, he was regarded by the English as a martyr, and miracles were said to have been worked at his tomb at Crowland. The earl left three daughters, the eldest of whom, Matilda, brought the earldom of Huntingdon to her second husband, David I of Scotland. One of Waltheof's grandsons was Waltheof (d. 1159), abbot of Melrose.