The District of Columbia Organic Act of 1871 is an Act of Congress that repealed the individual charters of the cities of Washington and Georgetown and established a new territorial government for the whole District of Columbia. Though Congress repealed the territorial government in 1874, the legislation was the first to create a single municipal government for the federal district.[1]
https://en.wikipedia.org/wiki/District_of_Columbia_Organic_Act_of_1871