"Without the NFL or a major sports betting holiday like March Madness a decline in April was a near certainty," said Joe Boozell, analyst for PlayIllinois.com. "The Illinois market faced a double-whammy with the return of in-person registration, which will eventually eat away at the market's ceiling even if it hasn't dramatically impacted handle yet. And there is no easy solution to that without a legislative fix."

Betting at Illinois' retail and online sportsbooks fell 15.2% to $537.2 million in April from the record $633.6 million in March, according to official data released Wednesday.

April's handle created $43.6 million in adjusted gross revenue, down from $44.3 million in March, yielding $6.5 million in state taxes and $527,100 in local taxes.

All but one U.S. market reported a month-over-month decline in April wagering. Of the 10 largest, Illinois' decline was shallower by percentage than all but New Jersey (-13%), Tennessee (-13.6%), and Pennsylvania (-14.4%).

Nearly all of those declines can be explained by the expected seasonal drop in sports betting, which typically begins in April and continues until the football season.

"Illinois is proving to be remarkably resilient as a market, overcoming the inconvenience of in-person registration at least temporarily," said Jessica Welman, analyst for the PlayUSA.com network, which includes PlayIllinois.com. "A concerted push before in-person registration went into place likely helped lessen the short-term effects, but it will be difficult for Illinois to keep pace with the nation's top markets over the long term."

Online wagering accounted for 95.5%, or $513.2 million, of all bets in April.

With the partial removal of the ban on wagering on in-state college teams the state legislature did give retail books something to look forward to when college football returns. But the ban will remain for online sportsbooks, which will mute the importance of the change.

"The change is a positive one, but it won't make a significant difference in the short-term," Boozell said. "Illinoisans overwhelmingly place their bets online. So, any change that only affects retail betting will be limited in its impact. Hopefully this will be an incremental step toward lifting the ban entirely."

FanDuel/Fairmont's online and retail sportsbooks attracted $177.8 million in bets, the first time FanDuel has topped the market. DraftKings/Casino Queen was second with $169.6 million in combined handle. Barstool/Hollywood Casinos was fourth with $51.4 million in its first full month of online operation.

"FanDuel catching DraftKings is a seismic shift in the dynamics of the market, and a credit to FanDuel's campaign to register bettors ahead of in-person registration," Welman said. "Barstool's push to register customers before in-person registration took effect made a difference, too. But it will be difficult to make significant inroads on the market leaders, which all had months of being able to register customers unencumbered."