Well they always point to the Organic Act of 1871 when talking about it and all that did was make Washington, D.C. an actual city (i.e. give governance rights to) and allow for us to sue the government iirc. The only other thing I can think of is 28 U.S. Code § 3002, but all that does is give the definitions for what each word means in the chapter it’s talking about (and only that specific chapter, not the whole thing).