Two clauses in the Constitution define federal jurisdiction:
(a) Article I, Section 8, Clause 17: “The Congress shall have the power to exercise
exclusive legislation, in all cases whatsoever, over such district (not exceeding ten miles
square) as may, by cession of particular States, and the acceptance of Congress, become
the seat of the Government of the United States; and to exercise like authority over all
places purchased by the consent of the Legislature of the State in which the same shall be,
for the erection of forts, magazines, arsenals, and other needful buildings…”
b) Article IV, Section 3, Clause 2: “The Congress shall have the power to dispose of
and make all needful rules and regulations respecting the territory or other property belonging to the United States…”
The territorial and legislative jurisdiction of the U.S. Congress extends to the ten square miles of Washington DC, military installations where States have explicitly ceded authority to the federal government, and U.S.
Territories such as Puerto Rico, Guam, American Samoa, and the Virgin Islands. In accordance, IRS income taxes apply (if they apply at all) to people who live and/or work in these areas, or who work for the federal government.