Blueprints For Old Sand Rails Are Blueprints Of All Homes Kept At City Hall? Where Might I Find My Home's Original Blueprint?

Are blueprints of all homes kept at city hall? Where might I find my home's original blueprint? - blueprints for old sand rails

I need information about where an owner can find the original plans for your home. Once I heard it on file in City Hall, but I wonder if my source knew what they were saying. It is logical that the city will have a copy, because we have received the permits before modifying our house. How can we know if we have not been altered or, if no original copies on file.