The Chicagoland Area does not have 1 club but a bunch of regional clubs via area. There are other smaller groups but these are the main groups. Illinois has ranked in the top 5 of courses, events, & PDGA members over the past few years. A lot of that has to do with the strong presence of these clubs. I'm guessing there are easily 1000+ members from these groups (paid members each year).
North Suburbs--DISContinuum
Northwest--DGU Streamwood
West--Fox Valley
South--J-Town
South--Basket Cases
North Suburbs--DISContinuum
Northwest--DGU Streamwood
West--Fox Valley
South--J-Town
South--Basket Cases