Adjusted gaming revenue from sports wagering for the month amounted to $36.2m (£26.2m/€30.6m), down 17.0% from $43.6m reported in April.
Online sports betting accounted for $34.4m of total sports betting revenue in May, while retail contributed $1.9m to the monthly total.
In terms of handle, player spending reached $506.7m in May, down 5.7% month-on-month from the $537.2m wagered by consumers in April.
Players bet a total of $482.1m with online sports wagering operators during the month, as well as $24.6m a retail sportsbooks across the state.