There is no national archive for plat maps in the United States. States and counties or townships within states maintain individual archives for plats and maps.
The National Archives retains over 10 million land sales and purchases for the 30 public land states. These do not include plats or township maps of areas; only the required paperwork to close a sale. The other 20 states maintain this paperwork on their own state archive systems.
The National Archives houses records for the western United States, and the Bureau of Land Management maintains various land tract records for the eastern United States.