When is Valentine's Day and why is it celebrated?

Valentines day is on February the 14th and is celebrated because a saint, named saint Valentine was in jail and while he was there he fell in love with the jailers daughter who was blind & on the day that he was suppose to be hanged, February the 14th, he sent one last love letter to the jailers daughter signed from your Valentines and that is why people write your valentines at the end of there cards and why its celebrated.