A listing of Irish Pubs can't be done without mentioning Celtic Crossing, simply the most 'real' Irish Pub in Chicago, but they have no food, save for Tato Crisps so mentioning them in the Eating Out category is out.
I didn't use the word 'authentic' 'cause I meant real.
As far as food, I second Celtic Knot, but in the city, The Gage rules and blows away the Knot's food. Excellent renditions of the standards like Shepherd's pie, Fish and Chips, Scotch Egg etc. But the roast elk saddle and other game entrees are awesome. I just noticed they have a 'house poutine' with elk ragout on the menu. I'm there, if not today, tomorrow.

Roast Saddle of Elk, The Gage
For pub crawling, I used to do 2 maps, one for
Lincoln Park, one for
River North, both where you could stumble from pub to pub and 2 or 3 blocks is as far as you need to go before finding another one (and also find plentiful cabs or public transportation, essential after more than 1 pub in a row). But in a city where a new one opens every month my maps are ancient, and in serious need of editing. The newest pub, D4 is nice, but the crowds are tourists, not Irish regulars, or at least not yet. Good mussels, good beer and scotch selection.
Celtic Crossing
751 N. Clark St.
Chicago, IL 60610
312-337-1005
http://www.thegagechicago.com/24 South Michigan, Chicago
D4345 E. Ontario, Chicago