Katherine Edgecombe (died 1553) was an English aristocrat and courtier. She was born Katherine St. John, a daughter of John St. John of Bletsoe and Sybil, a daughter or cousin of Rhys ap Morgan. She was the sister of John St. John who died in 1558. She first married Gruffydd ap Rhys ap Thomas. She was appointed to wait on Catherine of Aragon in October 1501. They served Catherine of Aragon and Prince Arthur at Ludlow Castle. Gruffydd ap Rhys died in 1521 and was buried near Prince Arthur at Worcester Cathedral. Their son, Rhys ap Gruffydd was executed for treason at the Tower of London in 1531.