Regardless of State law, it's considered "criminal possesion of a firearm". Having a license in your respective state doesn't exempt you from a felony prosecution in Federal court. Post offices, court houses, national parks....etc...INCLUDE parking lots...
Some states follow the Feds....some just require you to inform Ranger Ricky that you're carrying...CHECK your state regs...Believe it or not, MA lets me carry unless I'm actively hunting. Then, I cannot have any ammunition on my person that doesn't match the firearm I'm using at the time. NO EXCEPTIONS...!!!!!
It will affect the remainder of your life, conviction or not...ALWAYS talk to an attorney BEFORE you talk to anyone else...
Seems pretty silly...ya can't carry a firearm while touring the Springfield Armory!