Castillo was drafted by the Cubs in 1987 and played seven seasons there. During his career, he played 13 seasons total with the Cubs, Rockies, Tigers, Blue Jays, Red Sox and Marlins. He retired in 2005.
Authorities said divers are going to search Bartlett Lake in Arizona, near Castillo's house, to look for his body. Castillo was on a pontoon boat with a friend on the lake when he decided to go swimming. His friend called for help when he did not come up out of the water.
"It is impossible to express in words the level of sadness we feel due to this tragedy," his family said in a statement. "All of those who counted Frank as a personal friend, and to all those wonderful fans who cheered for him during his major league career, we genuinely appreciate your prayers and kind words during this extremely difficult time."