Not sure about exclusion and what not, but around here in WA, you can carry INTO the courthouse, but you have to check the weapon in. They like it that you get there a little early obviously, but you can carry into the courthouse you just have to let them know at the checkpoint. Some will give you false information if you call ahead, some are clueless about the law (and the safe answer for them is just plain no) and some are convinced it is illegal because it doesn't compute with them and they don't want to be bothered to look it up OR questioned by a civlian peon. In this case, you just have to call 'em out, get their boss. See, they have to provide this, it is in the law here. But there was a thread on here earlier this year about a guy given a hassle going in for jury duty downtown Seattle at the county courthouse. They lied to him, went so far as to threaten him, but it was all bluster.
Make sure your state is like this though. Our state has to either permit you to carry, or provide you with a check-in when passing through secure public areas. This does NOT apply to federal property, they've already got a defacto ban in place as it is.
No way I'd show up to jury duty any other way, and probably open carry too because it would be a good place I think to "protest" and actively promote the 2A in public. Most people think you can't carry there (you can't carry far) and that may be a plausible reasoning for Joe Blow civilian, but this ignorance extends to the folks enforcing this very law, the very guy at the check in! That kind of ignorance is simply unacceptable, how can a guy enforce laws he doesn't even know exist?
So summary: you can carry in the courthouses in WA, but not very far, they have to check it in, but chances are the guy at the check in will think it is for cops only, and your attempt at schooling him will be all for naught (they don't like their "authority" to be questioned) so just go straight to his boss and have him read the moron the actual law passed by legislature he should be enforcing and not the crap he made up that morning.
The advice from a 20+ year WA cop in Seattle: just leave it in the car, don't tread on that cop's ignorance, that it is better to do that than to argue your rights with a cop. Really? Really!? I'll check my pistol at the door, but I won't be checking my rights at the door, not now not ever, and that is why I would make such a bid deal out of carrying to the courthouse. I'm real quiet and discreet otherwise, but you question my rights and I'll up the anty.