The Patent Act permits a patent to be divided up regionally within the United States.
The applicant, patentee, or his assigns [may] grant and convey an exclusive right under his application for patent, or patents, to the whole or any specified part of the United States.
35 U.S.C. 261. The allowance for geographic division was added as part of the Patent Act of 1836 and overruled the very first Supreme Court patent law decision, Tyler v. Tuel, 10 U.S. 324 (1810). In Tyler, the Supreme Court found that a patent assignment excepting a few specific counties was not a “true assignment” and therefore the purported assignees had no right to sue on the case. The court suggested that exceptions might be found in equity.
If you are curious, the assignment excluded the counties of “Chittenden, Addison, Rutland and Windham, in the state of Vermont.”