If I am flying into O'Hare on KLM business class, will I have lounge access on arrival (I assume only the Delta SkyClub?)? I will booking another domestic flight the same day to get home, but only economy.

On arrival, no. T-5 has no arrival lounges. You will not have physical access to Departure lounges.

The OP will have access to depaurture lounges as he/she has onward travel.

Regardless, I sent an alert to the Mods to move this to the KLM forum where the question can best be answered.

It's also cross-posted in the Airport Lounges forum.

Regardless, the OP will not have lounge access on departure. KLM uses the Delta Sky Club at ORD.

The Sky Club Access & Policies for SkyTeam premium cabin passengers require that they be confirmed in First or Business class in all segments of their journey. The OP plans on departing ORD in Economy and doesn't specify which airline.

If I didn't have an additional flight after arriving in ORD on KLM business class, would I have lounge access on arrival? I was thinking Delta Skyclubs do have arrival access.

So there are two elements in play here:

1. Delta Sky Club access policy applicable to your specific situation. Some more knowledgeable can opine on Delta's complex and ever-vacillating lounge access policy as I don't have my old college calculus textbooks handy anymore for reference.

2. You need to be able to get to the door of the Sky Club in the first place. As an international arrival at ORD T5, you will proceed through US immigration, collect any checked bags and effectively be dumped curbside as if you had just walked in off the street. Depending on whether you have on onward flight, with which carrier, in which terminal, and whether or not you have checked bags to drop with the onward carrier would determine the practicality and feasibility of being able to get airside to T5 and access the door of the Sky Club.

The ORD Sky Club is beautiful and one of the best in the Delta system...I certainly don't blame you for wanting to try to check it out.

Delta Sky Club access questions are more likely to receive accurate answers in the Delta forum:

Nothing like believing you are helping, and realizing otherwise. Hope your trip goes well