Marriage and children
He married Agnes de Saint John (d.1340), a daughter of John Saint John (d. 1302) of Basing in Hampshire (by his wife Alice FitzPiers, daughter of Sir Reynold FitzPiers.) and a sister of John St John, 1st Baron St John (d. 1329) of Basing.
By his wife he had five sons and two daughters:
John de Courtenay (1300–1349), first son, Prior of Lewes and Abbot of Tavistock.
Hugh de Courtenay, 2nd/10th Earl of Devon (1303-1377), second son, who married Lady Margaret de Bohun, daughter of Humphrey de Bohun, 4th Earl of Hereford by Princess Elizabeth of Rhuddlan, daughter of King Edward I and Eleanor of Castile.
Lady Eleanor de Courtenay (c.1305–1330), who married John Grey, 3rd Baron Grey of Codnor (died 1392).
Robert de Courtenay (1309–1334) of Moreton Hampstead in Devon, third son.
Sir Thomas de Courtenay (c.1311-1362) of Wootton Courtenay, Somerset, and of Woodhuish, Brixham, Devon, fourth son, a military commander against the French. He married a great Somerset heiress, Muriel de Moels, the eldest of the two daughters and co-heiresses of John Moels, 4th Baron Moels, feudal baron of North Cadbury in Somerset. His wife's share of her paternal inheritance included the manors of Kings Carswell and Dunterton in Devon, and Blackford, Holton, and Lattiford in Somerset.
Baldwin de Courtenay (c.1313-1340), fifth son.
Lady Elizabeth de Courtenay (c.1313-c.1364), who married Bartholomew de Lisle, Lord Lisle (1311-1345).