Well....I know they're found at every state line too. Maybe that can help you in your quest. Good luck

What? Streets have to be numbered and they wanted the origination point(s) to have some sort of significance, that's all. Didn't work out, and instead it's kinda arbitrary. Like in Chicago, the "zero milestone" (not called that, but I guess it's the same thing) is at the intersection of State and Madison streets. It's downtown, and State is kinda important, but it's not like it's at City Hall or anything. Other than being downtown, it's arbitrary and has no meaning. Apparently, some people were trying to avoid that and failed.

Conspiracy? Really?