Article IV Section 3

New States may be admitted by the Congress into this Union; but no new States
shall be formed or erected within the Jurisdiction of any other State; nor
any State be formed by the Junction of two or more States, or parts of
States, without the Consent of the Legislatures of the States concerned as
well as of the Congress. 

The Congress shall have Power to dispose of and make all needful Rules and
Regulations respecting the Territory or other Property belonging to the
United States; and nothing in this Constitution shall be so construed as to
Prejudice any Claims of the United States, or of any particular State.