The comedian helped raise $1 million to rebuild his native beach town on New York's Long Island following Superstorm Sandy.
The "When Harry Met Sally" star made the announcement before hundreds of beachgoers Saturday. Crystal donated $112,000 of the gift. The remaining $888,000 is coming from money he helped raise at the annual Celebrity Fight Night fundraiser in March.
The funds were all donated to the city of Long Beach.
The new $44 million boardwalk is set to be completed by mid-July.
The former hurricane knocked out power to more than 8.2 million households, destroyed dozens of homes and killed at least 90 people in 10 states.
The Associated Press contributed to this report.