Given Marriott's smoke-free policy, an in-room fireplace in the loop area is likely a challenge. I've seen many Marriott's in New England with a Hearth room, a semi-public sitting area organized around a gas burning hearth adajent to the lobby/check-in area. Is that what you're hoping to find? In the Chicago area, there are Residence Inns with fireplaces in the Gatehouse. To make it easier, I think "fireplace" is another amenity that might be added to the Advanced Search list on Marriott.com.
The closest Marriott with an in-room fireplace is the Residence Inn Chicago Deerfield about 20 miles from the loop in Deerfield, IL I just happened to stumble across photos of their 2 bedroom duplex suite. Looks really cozy and inviting, too
Jerry I recently stayed at a very nice RI here in CA that had fireplaces, the faux kind, with an electric switch and instant on features. Given fire codes and spare the air alerts here in smoggy CA, it most likely a space heater with a flame that, to my untrained eye, looked very real.
In past years and at RIs there were those glue and wood logs in the fireplaces, the ones the drug stores sell, but this time the glass partition on the front was sealed shut, and no logs of any kind were ever going to enter.
There are DVDs of fireplaces burning that last for hours () you can buy or rent--just kidding. But ask if the fireplaces are faux or fire.