"Illinois is exploding at a pace we've never seen before, putting it on track to join the largest markets in the country by year's end," said Jessica Welman, analyst for PlayIllinois.com. "This wouldn't have been possible if lawmakers' original intentions were met. If Gov. J.B. Pritzker hadn't suspended the in-person registration mandate, as was originally required, there is no way Illinois could have reached these heights so soon."

Illinois sportsbooks drew $434.6 million in bets in October, according to official data released Thursday. That is up 42.4% from $305.2 million in September and the fourth largest handle among legal jurisdictions in the U.S., behind only New Jersey, Nevada, and Pennsylvania.

By comparison, it took New Jersey 16 months to surpass $430 million and Pennsylvania 23 months.

"Illinois has long been an intriguing market, but nobody expected this kind of start," said Joe Boozell, analyst for PlayIllinois.com. "The market is still nowhere near maturity and yet it may still challenge Pennsylvania and Nevada in the coming months. We projected the market to one day take in $10 billion in bets annually, and while that is still likely a few years away, it could come quicker than anyone dreamed, too."

With a sports schedule that included a full month of NFL football, the World Series, the NBA Finals, and the return of Big Ten football, October's bets yielded a whopping $42.2 million in adjusted gross revenue, up dramatically from $6.8 million in September. Those gains resulted in $6.3 million in state taxes.

Regional interest was a key contributor to October's results. Football led all sports by attracting $186.7 million in bets, up from $91.4 million.

"In every regulated market, when local teams do well a corresponding uptick in betting is expected, so it's not a surprise to see that in Illinois," Welman said. "That said, the weeks since October haven't been as kind for the Bears. But that early interest has been baked in, so it shouldn't get in the way of overall market growth."

Online sports betting accounted for 94.3% of all bets in October, or $409.8 million, and the three largest operators continue to dominate the market. DraftKings/Casino Queen led the market for the first time with $141.4 million in overall handle, including $138.5 million online, up from $95.9 million online in September. BetRivers/Rivers Casino continued to capitalize on its early launch with $115.5 million overall and $101.5 million online, up from $98.6 million online in September. FanDuel/Par-A-Dice Casino made gains, too, with $105.6 million overall and $105.2 million online.

"BetRivers has really done well in getting a head start on DraftKings and FanDuel, but holding off the two largest sportsbooks operators in the country is all but  impossible," Boozell said. "That said, with a bevy of new competitors set to launch in the coming months, the landscape should significantly change behind the state's three biggest operators."