The Fundationis et Fundatorum Historia of Forde Abbey names “Hugonem secundum…ac Philippum postea dominum de Mourton prope Dartmore” as sons of “Hugonem de Courtnay primum” & his wife. 
He succeeded his father in 1292 at Okehampton.  He was summoned to parliament 6 Feb 1299, whereby he is held to have become Lord Courtenay.  He was declared Earl of Devon 22 Feb 1335. 2
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son and heir, came of age in 1297.
Of Okehampton, Devon, Waddesdon, Buckinghamshire, etc.
He was heir in 1293 to his cousin, Isabel de Rivers, Countess of 
  Aumale and Devon.
He served in the Scottish wars, and was present at the Siege of Caerlaverock 
  Castle in 1300. 
He was knighted by the Prince of Wales 22 May 1306, a Banneret in 
  1308.
He was chosen one of the Lord Ordainers in 1313, and was a member 
  of the King's Council 9 Aug 1318. 
On 22 Feb 1334/5 he was declared Earl of Devon. 3 
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Inquisition Post Mortem (abridged). 4
273. Hugh de Courteneye or de Courtenay, late earl of Devon.
Writ... 3 January, 14 Edward III. [1340/1]London. Inq. Wednesday after St. Hilary, 14 Edward III.
  The parish of St. Dunstan within the bar of the New Temple in the 
    suburb of London. A messuage and five shops held of the king in 
    chief in free burgage, like the whole city of London.
Berks. Inq. 10 January, 14 Edward III (defaced)
  Sutton. The manor, with the advowson of the church, held [for life 
    by the enfeoffment of Eleanor de Courteneye] with remainder [to 
    Hugh his son and heir] of the king in chief by service of a knight's 
    fee.
  Heir as above.
Oxford. Inq. made at Nywenham, 12 January, 14 Edward III.
  Crawell. A toft held of the king in chief by service of a quarter 
    of a knight's fee.
Southampton. Inq. 14 January, 14 Edward III.
  Brommore and Lemyngton. The manors held for his life, by fine levied 
    in the court of King Edward II with the king's licence, with remainder 
    to Hugh his son and the heirs of his body...
  Heir as above.
Somerset. Inq. 12 January, 14 Edward III.
  Croukerne. A moiety of the manor held of the king in chief, as 
    parcel of his earldom of Devon; and the other moiety of the manor 
    and the h[undred of Crou]kern, with the knights' fees, advowsons 
    of churches &c. belonging to the said moiety, held as parcel 
    of his earldom of Devon by the grant of Eleanor, the wife 
      of Hugh de Courtenay, father of the said earl....; with 
    remainder to Hugh, son of the said earl, and the heirs of his body, 
    to hold the king and his heirs in chief for ever.
    Ivelcestre. A yearly rent of 100s. from certain free tenants 
    for a messuage and a carucate [of land] held of the king in chief 
    by service of a rent of 2s. yearly for the farm of Ivelcestre.
  Heir as above.
Dorset. Inq. 14 January, 14 Edward III.
  Ebrighton. The manor held of the king in chief as member and parcel 
    of his earldom of Devon.
    Iwerne Courteney. The manor held for his life as parcel of his barony 
    of Okampton, by the grant of Stephen de Haccumb... with remainder 
    to Hugh, son of the said earl, and the heirs of his body...
  Heir as above.
Devon. Inq. made at Exeter, 10 January, 14 Edward III. (defective)
  Devon county. 18l. 6s. 8d. pertaining 
    to his earldom of Devon, to be received yearly by the hands of the 
    sheriff of the county from the issues of the county.
    Honyton. The manor with the borough...
    Kadelegh. The manor...
    Exemynstre. The hundred...
    Buddelegh. The hundred held of the king in chief at fee farm, to 
    himself and to his heirs...
    Nywnham by Chilmelegh. A . . . . messuage, lands and rent, held 
    of the king in chief, as parcel of the barony of Okhampton.
    Huntebere by Ailesbere. Certain lands and tenements...
    Northpole. A carucate of land, including a capital messuage, held 
    of the heir of John de Clavill...
    Plympton. The castle, manor, and honour, with the [manors] of Twyverton, 
    Exemynstre and Thoppsham, and the hundreds of Plympton, Twyverton, 
    Harrygge and Wonford, with free fishery in the Exe, together with 
    the knights' fees and the advowsons of churches belonging to the 
    said castle, manor, and honour [of Plympton], held of the king, 
    as of the right of his earldom of Devon, by the grant of Eleanor, 
      late the wife of Hugh [de] Courteney his father,... with 
    remainder to Hugh the son, and the heirs of his body...
    Okampton. The castle, manor, and honour, with the manors of Saunford 
    Courteney, Chalvelegh, Deulton, Ken, Wympel and Ailsbere, and the 
    hamlet of Nywton Popeleford, and three mills in the Exe by Ex[eter 
    with] the advowson of the church of Throulegh, together with the 
    knights' fees and advowsons of churches belonging to the said castle, 
    manor, and honours, held for his life of the king, by barony, by 
    the grant of the aforesaid Eleanor....
    Chilmelegh. The manor, with the advowson of the church, the advowson 
    of the church of Ken, and of the prebends of Heyes, Cotiton, and 
    Ken, in the chapel of the Blessed Mary in the castle of Exeter...
  Heir as above.
Writ of certiorari de feodis &c. to the escheator in 
  cos. Somerset, Devon, &c., 3 January, 14 Edward III.Devon. Inq. 10 January, 14 Edward III.
  The advowsons of the churches of Honyton, Cadelegh, Stoke Dauumarle, 
    Wodelegh, St. Leonard's by Exeter and Milton Dauumarle.
Writ to the escheator in cos. York, Northumberland, Cumberland 
  and Westmoreland, 3 January, 14 Edward III.Cumberland. Extent, Saturday after the Annunciation, 15 
  Edward III.
  He held no lands &c. in the counties aforesaid, as the jury 
    understand, on the day he died.
    Brigham. The advowson of the church held, as of his own right, of 
    Antony de Lucy, as of the honour of Cokermuth, which is in the hand 
    of the said Antony, by the grant of King Edward II...
    He had no fees in the said counties on the day he died.
  Hugh his son, aged 23 and more, is his next heir.
C. Edw. III. File 62. (4.)
  E. Enrolments &c. of Inq. Nos. 31 and 32.