In Iowa, all schools are "weapons free zones". I think it is ridiculous, but my opinion is a bit different than many, obviously.

Any Federal courthouse or office building. The US Post Office (or any other USPS facility) is also a "weapons free zone". Almost any government building of any kind at this point, really. Even some of the county courthouses have metal detectors and policies such as these.

The Iowa State Fair has a no weapons policy as well, though folders with pocket clips were as common as ball caps with agricultural logos on them.

I wear one anytime and all the time, unless I have to go somewhere that expressly forbids it, such as the examples in this thread. I have been given a hard time about carrying a "weapon" at some church things, but I politely point out that it is more of a decoration, and a tool, than a weapon, and that I could hurt you just as easily with the ball point pen in my shirt pocket, if that were my intent.

Of course I am a professional bladesmith, vocationally making knives and swords for 21 years, so I am seldom without a cutting tool.

It is best to know the letter of the law where you live. Get thee to the library, and look it up. Generally, though, weapons laws are written such that it is mostly up to the discretion of the officer on the scene what to do. It is best to be polite, in all cases, and carry one's self with calm and confidence.