The festivities included a Marine Corps band, a 21-gun salute and the placing of an official White House wreath on Reagan's grave.
The keynote address was delivered by former Mississippi Gov. Haley Barbour, who was a political aide to the late president.
Admission to the library was free on Monday, which marks the second Ronald Reagan Day in California under a 2010 law written by former state Sen. George Runner.
The law established Feb. 6 as a special day to honor Reagan. The bill did not create a state holiday and does not cost taxpayers money.
City News Service contributed to this report.