Update: Nov 2015 O'Hare International Airport now offer traveling breastfeeding and breast pumping moms a lovely nursing mothers lounge. This airport lactation room is located in Terminal 3 Rotunda, next to the Yoga Room and Urban Garden.
Mom Laura wrote: "Ohare's nursing rooms finished and it's lovely. There's a private chair and a sink area. It's located in terminal 3 on the second floor of the rotunda. They keep it unlocked though."
As an Option if you're not near the Nursing Mothers Lounge and need to breastpump/breastfeed, Travelers Aid whose main office is in Terminal 2 next to the 'Kids on the Fly' exhibit will happily welcome breastfeeding mothers and offer up a private, comfortable space to breastfeed. Their hours are as follows: