Illinois has at least 70 Century Club Companies, 11 of which are public. 84% of the state's companies over 100 years old are privately owned and of those, 47 are generational family firms. Here is the list - please leave a comment if you see an error or if you know of a company in continuous, independent operation for over 100 years that should be added to this list.
1834: Galena Gazette Publications, Galena
1837: Deere & Company, Moline public
1838: Comstock-Castle Stove, Quincy 6th generation
1845: Brunswick, Mettawa public
1848: Knapheide Manufacturing, Quincy, 6th generation
1848: Maze Lumber, Peru, 6th generation
1854: Hoskins Building Center, Elizabeth
1855: Baird & Warner, Chicago 5th generation (real estate services)
1857: Iwan Ries & Co., Chicago 5th generation (tool manufacturing)
1857: Klein Tools, Lincolnshire, 5th generation
1857: Zengeler Cleaners, Northbrook, 5th generation
1864: R.R. Donnelley & Sons, Chicago public (printing & publishing)
1865: American Hotel Register, Vernon Hills, 3rd & 4th generations (manufacture hospitality products)
1865: Law Jones Funeral Home, Savanna 2nd generation
1870: The Tablet & Ticket Company, West Chicago 5th & 6th generations (display & signage products)
1873: Follett, Westchester 5th generation (publisher educational products)
1873: George J Rothan, Peoria 5th generation (custom millwork)
1875: Anderson's Bookshops, Naperville 5th generation
1875: Oswald's Pharmacy, Naperville 6th generation
1876: RR Street & Co, Naperville/Chicago private (cleaning products)
1880: Citizens State Bank, Lena public
1881L Kennicott Brothers, Chicago 100% employee-owned (floral distributor)
1882: Siemer Milling, Teutopolis 4th generation + ESOP
1885: Cretors, Wood Dale 5th generation (manufacture popcorn machines)
1886: Gonella Baking, Schaumburg 4th generation
1887: John Boos & Co., Effingham 3rd generation? (manufacture butcher block)
1888: Abbott Laboratories, Abbott Park public
1888: Louis Glunz Beer, Lincolnwood 3rd, 4th & 5th generations
1888: Matot, Bellwood 4th generation (manufacture dumbwaiters)
1889: Northern Trust, Chicago public
1890: A.M. Castle & Co., Oak Brook public (metals distribution)
1890: Great Lakes Dredge & Dock, Oak Brook public
1891: Alexander Lumber, Aurora 4th generation
1891: Bulley & Andrews, Chicago 4th generation (construction)
1892: Lambrecht's Jewelers, Wilmette 4th generation
1893: Moline Wheel, Moline 3rd generation
1893: Vienna Beef, Chicago
1894: Miner Enterprises, Geneva (manufacture rail car components)
1895: Stanford Grain, Stanford (agricultural co-op)
1896: Ed Miniat, South Holland, 4th generation (meat wholesaler)
1896: Tootsie Roll Industries, Chicago public + 2nd generation
1897: Glik's, Granite City 4th generation (retail apparel)
1898: American Nickeloid, Peru (manufacture metal products)
1898: Vita Food Products, Chicago
1899: Galloy & Van Etten, Chicago (stone cutting) 4th generation
1903: Morton Buildings, Morton employee-owned
1905: Earlville Farmers' Coop Elevator, Earlville
1905: Horween Leather, Chicago 4th & 5th generations
1906: Kirchner Building Centers, Kansas 4th generation
1906: Sloan Valve, Franklin Park 4th generation (manufacture plumbing systems)
1908: C.C. Wagner, Summit 5th generation (lumber & building products)
1911: Milledgeville Home Center, Milledgeville
1912: Illinois Tool Works, Glenview public
1912: Lemfco, Galena 5th generation (manufacture iron castings)
1913: ILMO Products, Jacksonville 4th generation (wholesale industrial gases)
1914: DaValle Jewelers, Harwood Heights 3rd generation
1914: deBuhr's Seed & Feed, Mattoon family-owned
1914: IRMCO, Evanston 4th generation (industrial lubricants)
1914: Mechanical Devices, Bloomington 3rd generation
1914: P.J. Hoerr, Peoria 3rd generation (construction)
1914: Vogue Tyre & Rubber, Mount Prospect
1914: Waukegan Roofing, Wheeling
1916: Boeing, Chicago public (HQ moved from Seattle 2001)
1916: Ideal Industries, Sycamore 4th generation (manufacture tools)
1917: Chicago Clock, Clarendon Hills 4th generation (retail clocks)
1917: Fellowes Brands, Itasca 4th generation (manufacture office products)
1917: Radio Flyer, Chicago 3rd generation
1918: Orlando Auto Top, Chicago family-owned
1918: Pearl City Elevator, Pearl City agricultural co-op
1919: ConAgra, Chicago public
1919: Crescent Electric Supply Company, East Dubuque 3rd generation? (wholesale electrical products)
1919: Elgin Industries, Elgin 3rd generation (manufacture vehicle components)
1919: Griffith Foods, Alsip 4th generation (food products)
1919: Michuda Construction, Tinley Park, 5th generation
1919: Wahl Clipper, Sterling 3rd & 4th generations (manufacture personal grooming products)
1920: Darvin Furniture, Orland Park 3rd generation (retail mattresses)
For more information about how these and other Century Club Companies have survived over the decades, see my book: Lessons from Century Club Companies: Managing for Long-Term Success available in paperback or as an ebook from Amazon or Barnes & Noble