January revenue for the three casinos was 13.1 percent lower than the revenue they reported in December.
MGM Grand Detroit was the only one of the three to see an increase, reporting a 1.1 percent rise to $46.7 million for the month, when compared to the same month last year.
Revenue was down 2.4 percent to $37.1 million for MotorCity Casino Hotel and 5.7 percent, dropping to $25.2 million for Greektown Casino-Hotel, when compared with January 2015 results, the Gaming Control Board said.
MGM had 43 percent of the market in January, MotorCity had 34 percent and Greektown had 23 percent.
The three Detroit casinos paid $8.8 million in state taxes in January, compared with $9 million for the year-earlier month.
And they reported submitting nearly $13 million in wagering taxes and development agreement payments to the city of Detroit during January, according to the board.