The bets will be down before the ball goes up this week when the NCAA Basketball Tournament begins.

The American Gaming Association estimates that “around one-quarter of American adults — or 68 million people” will “wager $15.5 billion” as March Madness works itself into a fever pitch.

Illinoisans will be well represented in the scrum of in-person and online betting, according to a recent report by the state’s legislative Commission on Government Forecasting and Accountability.

“Illinois has become one of the biggest markets in sports wagering in the United States,” stated commission research analyst Austin Verthein.

That finding doesn’t just represent a new social activity — one with positive and negative consequences — but a growing revenue source for financially challenged Illinois.

Illinois was one of a number of states that rushed to legalize sports gambling after the U.S. Supreme Court opened the door with a 2018 ruling.

As a consequence, Verthein said Illinois’ decision in 2020 “has allowed the state to reap the benefits ahead of the nationwide curve.”

The “benefits” cited by the report are “adjusted gross receipts” taxed “at a flat 15 percent rate.” Most of that revenue goes to finance capital projects.

Sports waging is just one arena of gambling state officials have embraced.

The state began decades ago with betting on horse racing — an activity whose popularity has sharply declined. That was followed by the state lottery.

Since then, Illinois has legalized casinos, off-track horse-race betting and video gambling, and followed those decisions with expansions of the status quo.

One of the latest moves by Gov. J.B. Pritzker and the Legislature has been to expand the allowable number of casinos, permit racetracks to host other forms of gambling (“racinos”) and, for the first time, authorize a huge casino in Chicago.

Locally, Danville will host a casino that’s currently under construction.

Given the popularity of sports gambling, the legislative commission contends that the Illinois boom will continue as “marketing increases and as more sports wagering platforms develop.”

Sports betting in Illinois got off to a slow start in 2020, largely attributable to the coronavirus pandemic that shut down businesses, kept people out of circulation and limited the number of sports events.

Adjusted gross receipts in 2020 totaled $125.5 million. That number jumped in 2021 to $525.1 million and further increased to $795 million in 2022.

Although those numbers generate substantial revenues in the aggregate, sports-gambling-related tax receipts — in fact, all gambling tax receipts — represent helpful chump change in the context of the state’s roughly $50 billion annual budget.

Still, Illinois legislators have grasped for new gambling revenues like a drowning man lunges for a life preserver.

Why? They want the revenue. More important, there’s little resistance to levying taxes on activities in which otherwise-tax-averse citizens voluntarily participate.

Although March Madness is dominated current wagering, football represents the big dog. The legislative commission reports that “the three record months in adjusted gross revenues occurred from October 2022-December 2022 during the football season, sports wagering’s primary driver.”

Those three months in 2021 generated $52.6 million, $79.3 million and $33.7 million, respectively. That compares with $102.1 million, $978 million and $82.4 million in 2022.

Over the past three years, Illinois has raised $216.8 million in revenue from sports betting — $18.8 million in 2020, $78.8 million in 2021 and $119.3 million in 2022.

The commission’s report stated that — “if current trends hold” — Illinois “should expect tax revenue” to “well eclipse $100 million in 2023.”