Richard of Cornwall married three times and had six legitimate children, none of whom themselves had children, but he did have illegitimate progeny:
His first wife, Isabel Marshal (d.1240), whom he married on 30 March 1231 at Fawley, Buckinghamshire, was the daughter of William Marshal, 1st Earl of Pembroke by his wife Isabel de Clare, daughter of Sir Richard "Strongbow" de Clare and Aoife MacMurrough.
Isabel died on 17 January 1240 while giving birth at Berkhamsted Castle and was buried at Beaulieu Abbey.
By Isabel Marshal he had four children, of whom only one reached adulthood:
John of Cornwall (31 January 1232 – 22 September 1232), born and died at Marlow, Buckinghamshire, buried at Reading Abbey.

Isabel of Cornwall (c. 9 September 1233 – 6 October 1234), born and died at Marlow, Buckinghamshire, buried at Reading Abbey.

Henry of Cornwall (2 November 1235 – 13 March 1271).
Known as "Henry of Almain" (Germany), he was murdered by his cousins, the Montfort brothers Guy and Simon the Younger, in revenge for the beheading of their father and older brother at the Battle of Evesham.
He was buried at Hailes Abbey in Gloucestershire.
He had no children.

Nicholas of Cornwall (b. & d. 17 January 1240 at Berkhamsted Castle), died shortly after birth, buried at Beaulieu Abbey with his mother.

His second wife, Sanchia of Provence (c.1225 – 9 November 1261), whom he married in Westminster Abbey on 23 November 1243, nearly four years after the death of his first wife, was the daughter of Ramon Berenguer IV, Count of Provence by his wife Beatrice of Savoy.
Sanchia was the third of four sisters; her elder sisters were the Queens of France and England, and her younger sister later became Queen of Sicily.
The match was arranged by Sanchia's elder sister Queen Eleanor, wife of Richard's elder brother King Henry III of England.
Sanchia died on 9 November 1261 at Berkhamsted Castle and was buried 15 November in Hailes Abbey in Gloucestershire.
By Sanchia of Provence Richard had a further two sons:
unnamed son (Jul 1246 – 15 Aug 1246), died in infancy.

Edmund, 2nd Earl of Cornwall (26 December 1249 – before 25 September 1300), usually styled Edmund of Almain.
Edmund married Margaret de Clare (1250 – shortly before Nov 1312), daughter of Richard de Clare, Earl of Gloucester by his second wife Maud de Lacy, daughter of John de Lacy, 2nd Earl of Lincoln.
Edmund and Margaret had no children.
Their marriage was annulled in February 1294.

 
Richard's third wife, Beatrice of Falkenburg, whom he married on 16 June 1269 at Kaiserslautern, was the daughter of Dietrich I, Count of Falkenburg, of Valkenburg Castle in the Netherlands, and was said to be one of the most beautiful women of her time.
Her father was a supporter of Richard's claim to the throne of the Holy Roman Empire.
The two men fought on the same side in a battle, at which time Richard met Beatrice and grew besotted by her.
There was a very large difference in age between them: at the time of their wedding in 1269, she was about fifteen years old whereas he was in his sixty-first year.
Indeed, the youngest of Richard's children was only four years older than Beatrice.
Richard doted on his young wife, and she had a high regard for him, but they produced no children.
Beatrice survived Richard by only five years and never married again.
She died on 17 October 1277 and was buried before the high altar at the Church of the Grey Friars in Oxford.

Richard also had several documented out-of-wedlock children.
 One of Richard's mistresses was Joan de Vautort, widow of Ralph de Vautort (d.1267), feudal baron of Harberton, Devon and Trematon, Cornwall.
Joan later married Sir Alexander Okeston, lord of the manor of Modbury in Devon, which manor, part of the Vautorts' feudal barony of Harberton, had been granted him by Roger de Vautort.
Joan bore her second husband a son and heir, Sir James Okeston.

By Joan de Vautort or other mistresses, the Earl of Cornwall had three sons and two daughters as follows:
Philip of Cornwall, a priest.

Sir Richard of Cornwall, who received a grant from his half-brother
Richard of Cornwall married three times and had six legitimate children, none of whom themselves had children, but he did have illegitimate progeny:
His first wife, Isabel Marshal (d.1240), whom he married on 30 March 1231 at Fawley, Buckinghamshire, was the daughter of William Marshal, 1st Earl of Pembroke by his wife Isabel de Clare, daughter of Sir Richard "Strongbow" de Clare and Aoife MacMurrough. Isabel died on 17 January 1240 while giving birth at Berkhamsted Castle and was buried at Beaulieu Abbey. By Isabel Marshal he had four children, of whom only one reached adulthood:
John of Cornwall (31 January 1232 – 22 September 1232), born and died at Marlow, Buckinghamshire, buried at Reading Abbey.
Isabel of Cornwall (c. 9 September 1233 – 6 October 1234), born and died at Marlow, Buckinghamshire, buried at Reading Abbey.
Henry of Cornwall (2 November 1235 – 13 March 1271). Known as "Henry of Almain" (Germany), he was murdered by his cousins, the Montfort brothers Guy and Simon the Younger, in revenge for the beheading of their father and older brother at the Battle of Evesham. He was buried at Hailes Abbey in Gloucestershire. He had no children.
Nicholas of Cornwall (b. & d. 17 January 1240 at Berkhamsted Castle), died shortly after birth, buried at Beaulieu Abbey with his mother.
His second wife, Sanchia of Provence (c.1225 – 9 November 1261), whom he married in Westminster Abbey on 23 November 1243, nearly four years after the death of his first wife, was the daughter of Ramon Berenguer IV, Count of Provence by his wife Beatrice of Savoy. Sanchia was the third of four sisters; her elder sisters were the Queens of France and England, and her younger sister later became Queen of Sicily. The match was arranged by Sanchia's elder sister Queen Eleanor, wife of Richard's elder brother King Henry III of England. Sanchia died on 9 November 1261 at Berkhamsted Castle and was buried 15 November in Hailes Abbey in Gloucestershire. By Sanchia of Provence Richard had a further two sons:
unnamed son (Jul 1246 – 15 Aug 1246), died in infancy.
Edmund, 2nd Earl of Cornwall (26 December 1249 – before 25 September 1300), usually styled Edmund of Almain. Edmund married Margaret de Clare (1250 – shortly before Nov 1312), daughter of Richard de Clare, Earl of Gloucester by his second wife Maud de Lacy, daughter of John de Lacy, 2nd Earl of Lincoln. Edmund and Margaret had no children. Their marriage was annulled in February 1294.
 
Richard's third wife, Beatrice of Falkenburg, whom he married on 16 June 1269 at Kaiserslautern, was the daughter of Dietrich I, Count of Falkenburg, of Valkenburg Castle in the Netherlands, and was said to be one of the most beautiful women of her time. Her father was a supporter of Richard's claim to the throne of the Holy Roman Empire. The two men fought on the same side in a battle, at which time Richard met Beatrice and grew besotted by her. There was a very large difference in age between them: at the time of their wedding in 1269, she was about fifteen years old whereas he was in his sixty-first year. Indeed, the youngest of Richard's children was only four years older than Beatrice. Richard doted on his young wife, and she had a high regard for him, but they produced no children. Beatrice survived Richard by only five years and never married again. She died on 17 October 1277 and was buried before the high altar at the Church of the Grey Friars in Oxford.
Richard also had several documented out-of-wedlock children.  One of Richard's mistresses was Joan de Vautort, widow of Ralph de Vautort (d.1267), feudal baron of Harberton, Devon and Trematon, Cornwall. Joan later married Sir Alexander Okeston, lord of the manor of Modbury in Devon, which manor, part of the Vautorts' feudal barony of Harberton, had been granted him by Roger de Vautort. Joan bore her second husband a son and heir, Sir James Okeston.
By Joan de Vautort or other mistresses, the Earl of Cornwall had three sons and two daughters as follows:
Philip of Cornwall, a priest.
Sir Richard of Cornwall, who received a grant from his half-brother 
Richard of Cornwall