Actual LAW that created
CORPORATION UNITED STATES
See “Acts of the Forty-first Congress,” Section 34, Session III, chapters 61 and 62 for establishment of CORPORATION UNITED STATES to govern Washington DC (only) on February 21, 1871.
Link:
https://www.loc.gov/law/help/statutes-at-large/41st-congress/session-3/c41s3ch62.pdf