From A Wiki of Ice and Fire
|Book||The Hedge Knight (appears)|
Ser Jon Penrose was a knight from House Penrose during the reign of King Daeron II Targaryen.
Jon took part in the tourney at Ashford Meadow in 209 AC, where he challenged Ser Tybolt Lannister, the heir of Casterly Rock. Ser Tybolt was unhorsed and broke his sword in his fall, but fought back with shield alone to win the bout.
It is unclear how Jon is related to the other members of House Penrose.