When I try and add oil to my 1997 Jeep Cherokee, it over flows.

Are you adding oil into the correct place? In this picture of the six cylinder engine, the yellow oil cap is in the center of the valve cover. - - - - - - - http://images.gtcarlot.com/pictures/54126458.jpg

If you have a V8, the yellow oil cap is on the passenger side valve cover at the front end. http://static.cargurus.com/images/site/2008/02/25/14/33/1997_jeep_gran d_cherokee_4_dr_limited_4wd_suv-pic-24455.jpeg

What are you seeing on the dip stick? Is there a possibility that the engine is full of oil? How much oil have you added?

'97 Cherokee (2.5L I4 - 4.5qts, 4.0L I6 - 6qts both 10W-30 oil) or Grand Cherokee (4.0L I6 - 6qts, 5.2L V8 - 5qts both 10W-30 oil).

You may have broken off that "ratcheting" part of the cap, leaving behind the rubber plug in the fill hole. You can remove that rubber plug with pliers until you can get another one at the junkyard, or buy a new one on Ebay for $10 like I did. My jeep is a 1999 GC with the six cylinder engine.