| Isabel Marshal | |
|---|---|
| Countess of Hertford; Countess of Cornwall | |
 | |
| Born | 9 October 1200 Pembroke Castle, Wales |
| Died | 17 January 1240 (aged 39) Berkhamsted Castle, Hertfordshire, England |
| Burial | |
| Spouse | Gilbert de Clare, 4th Earl of Hertford (m. 1217–30; his death) Richard, 1st Earl of Cornwall (m. 1231–40, her death) |
| Issue | Agnes de Clare Amice de Redvers, Countess of Devon Richard de Clare, 6th Earl of Hertford Isabel de Brus, Lady of Annandale William de Clare Gilbert de Clare Henry of Almain |
| Father | William Marshal, 1st Earl of Pembroke |
| Mother | Isabel de Clare, 3rd Countess of Pembroke |
Isabel Marshal (9 October 1200 – 17 January 1240) was a medieval English countess. She was the wife of both Gilbert de Clare, 4th Earl of Hertford and 5th Earl of Gloucester and Richard, 1st Earl of Cornwall (son of King John of England). With the former, she was a great grandmother of King Robert the Bruce of Scotland.