Valbuena, a 26-year-old, was claimed off waivers by the Cubs on April 4 after he was designated for assignment by the Toronto Blue Jays. He batted .303 with 31 RBI and 38 runs scored in 58 games. Valbuena will don the number 24 with the Cubs.
Castillo, 25, was off to a slow start, hitting .185 in seven games with the Cubs. He was injured on May 22 while blocking what was Kerry Wood's final pitch in a Cubs uniform, a curveball which struck out Dayan Viciedo of the Chicago White Sox.
In his second stint as a Cub, Hill was batting .179 in 11 games. At the time of the Cubs' trade for Hill, he was playing with the Cincinnati Reds' Double-A squad.
The Chicago Cubs' 40-man roster currently stands at 40 players.