Robert of Lexinton or Lessington (died 29 May 1250) was a British judge and administrator.
Robert of Lexinton was a son of Richard of Lexinton (probably the first son, according to the Oxford Dictionary of National Biography, probably the second according to the Dictionary of National Biography.
His father for a time administered the manor of Laxton (formerly Lexington, from whence the family's name derived. Robert's brothers included Henry of Lexington, sometime Bishop of Lincoln, and Stephen of Lexington, a Cistercian monk and abbot of Clairvaux abbey. He made his start as a clerk to a successor of his father as keeper of the manor of Laxton, one Brian de Lisle.
In 1214 he was appointed as a prebendary of the collegiate church of Southwell, and later succeeded to the barony of his father, who was alive in 1216. By 1221, he was acting as a justice in seven counties, and comes to notice in February 1221 as the author of a letter to Hubert de Burgh informing him of the route taken by the rebel Earl of Aumale and of the measures that he had adopted to secure the safety of the border. He continued to be employed in a like capacity in later years, being in 1225 the head of six judicial commissions.
He was warden of the honour and castle of Peak and governor of Bolsover Castle in Derbyshire, and also had charge of Orford Castle. He is described as a justice ‘de banco’ in 1226, and as one of the chief members of the king's court, or bench, in 1229, when he sat with other judges at Westminster to hear the case between the convent and the townsmen of Dunstable. There is reason to suppose that in 1234 he was the senior of the justices of the king's bench. In 1239 he is said to have been elected to the see of Lichfield, but, the right of election being then in dispute between the canons of Lichfield and the monks of Coventry, to have declined it.