January's winnings were down 0.7 % from the same month in 2010.
"There were a lot of positive metrics. The numbers just didn't come in like we had anticipated," said Mike Lawton, Senior Control board analyst.
One reason was a big drop in baccarat play, a high-roller game favored by Asian players.
The amount wagered was US$ 595.2 million, down US$ 243.1 million or 29 % from the same month last year, the report said. Moreover, those who did bet on baccarat were luckier than the house. Casinos won US$ 65.1 million on the game, down nearly US$ 43 million or 40 %.
Without baccarat, the statewide total win would have been up 4.8 % or US$ 37 million.
Casinos on the Las Vegas Strip, the economic engine that fuels Nevada's gambling and tourism economy, won US$ 482.7 million in January, down 2.5 %.
The decline was surprising for a month that had the UFC title fight between Frankie Edgar and Gray Maynard at the MGM Grand, and four conventions, including the Consumer Electronics Show.
The "win" figure is what was left in casino coffers after gamblers wagered US$ 10.8 billion at slots and table games. A breakdown shows the amount wagered at games totaled US$ 2.3 billion, down 13 %, and US$ 8.5 billion at slots, down 2 %.
For the fiscal year that began July 1, statewide casino wins are up 1.2 %.
Elsewhere in the state, casinos in Washoe County, which includes Reno, won US$ 57.2 million, down 4.9 %. Winnings were up 2 % in Elko County; 10 % in the Carson Valley; and 8.3 % in downtown Las Vegas. They were down 7.8 % at South Lake Tahoe.
On the bright side, the report showed taxes collected on the casino wins totaled US$ 68.8 million, up more than 15 %. Collections often don't correlate with month win figures because casinos pay taxes after they collect wagers made on credit.