Reagan's father was a nominal Catholic. Reagan's mother was a devout member of the Disciples of Christ and Ronald Reagan was raised in the denomination. Reagan attended Eureka College, which is affiliated with that denomination. Reagan himself was a Presbyterian as an adult. Reagan said that in temperment and religious beliefs he took after his mother. (Source: http://members.aol.com/_ht_a/willricci/reagan/)
From: "Ronald Reagan Facts" page on the Ronald Reagan Presidential Foundation & Library website (http://www.reaganfoundation.org/programs/lc/reagan_facts.asp):
Although raised in his mother's Disciples of Christ denomination, beginning in 1963 Reagan generally attended Presbyterian church services at Bel-Air Presbyterian Church, Bel-Air, California. He became an official member of Bel-Air Presbyterian after leaving the Presidency. In addition, Reagan stated that he considered himself a "born-again Christian."