The state Gaming Enforcement Division imposed the fine on Bally's Atlantic City on Jan. 23.
The decision was made public on Monday.
Bally's did not respond to a request for comment, but the division noted both sides had agreed to the penalty under a settlement.
Officials say the casino served a 17-year-old and an 18-year-old three alcoholic beverages without asking for identification on Aug. 21.
Within an hour, a casino security found the 17-year-old visibly intoxicated on the casino floor, and called an ambulance.
The minimum age for drinking - and gambling - in New Jersey is 21.