There's actually two different Xmas events with this most ubiquitous of Xmas concepts.
1)Three uptown/north center bars in Chicago have joined forces to carry over 20 different Christmas beers. This event continues through December 20th.
Mrs. Murphy & Sons Irish Bistro, 3905 N. Lincoln Ave., Chicago (773) 248-3905
Fountainhead, 1970 W. Montrose Ave., Chicago (773) 697-8204
Bar on Buena, 910 W. Buena Ave., Chicago, (773) 525-8665
Breweries: Anchor, Mikkeller, Petrus, J. K. Skrumpy's, Port Brewing, Jolly Pumpkin, Breckenridge, St. Feuillien, Sierra Nevada, Brasserie Dupont, Ridgeway, Delirium, The Bruery, Southampton Publick House, Tournay, Great Lakes, Affligem, Brasserie De Silenrieux, and more
Trolley service will take people between the bars on December 20th from 6 to 10pm.
2) And from the Flossmoor Station brewery blog:
This year we will again be doing our "12 Beers of Christmas". On December 12th for 12 days straight, Flossmoor Station Brewery will release a one-of-a-kind, completely unique beer especially for that day. We will tap the beer when we open and when it is finished, we'll have the next day to look forward to!
•Sunday, December 12 - Cinnamon IPA
•Monday, December 13 - Vanilla Bean Brown
•Tuesday, December 14 - Ginger Marzen
•Wednesday, December 15 - Licorice Stout
•Thursday, December 16 - Spruced Red
•Friday, December 17 - Chocolate Cherry Brown
•Saturday, December 18 - Wassail Wheat
•Sunday, December 19 - Clove Red
•Monday, December 20 - Mint Stout
•Tuesday, December 21 - Juniper Gandy
•Wednesday, December 22 - Chocolate Magnolia