This Chicago DUI lawyer has posted on DUI's in Illinois here. She's also posted on DUI's throughout the Midwest here and here. Now comes a bit of human geography that may explain it.
From consumerist.com( via floatingsheep.org) :
Starting in Illinois, the beer belly expands up into Wisconsin and first spreads westward through Iowa/Minnesota and then engulfs Nebraska, and the Dakotas before petering out (like a pair of love handles) in Wyoming and Montana.FWIW- Wisconsin comes in third for bars per 10,000 people. It's hard though to be certain that the number of bars noted is accurate because in many small towns and trout hamlets the bar serves as a gathering spot for entire families and communities.
The clustering was so apparent that we wanted to check how it compared to the "official" data on this activity. So we gathered 2007 Census Country Business Pattern on the number of establishments listed in NACIS code 722410 (Drinking places (alcoholic beverages)) and divided by Census estimates for state population totals for 2009 and found remarkable correspondence with our data.
On average there are 1.52 bars for every 10,000 people in the U.S. but the states that make up the beer belly of America are highly skewed from this average.