United States Code/Title 4/Chapter 3
§ 71. Permanent seat of Government
All that part of the territory of the United States included within the present limits of the District of Columbia shall be the permanent seat of government of the United States.
§ 72. Public offices; at seat of Government
All offices attached to the seat of government shall be exercised in the District of Columbia, and not elsewhere, except as otherwise expressly provided by law.
§ 73. Same; removal from seat of Government
In case of the prevalence of a contagious or epidemic disease at the seat of government, the President may permit and direct the removal of any or all the public offices to such other place or places as he shall deem most safe and convenient for conducting the public business.