The fact that the united states federal government has a DUNS d&b number shows that it is indeed incorporated.

https://www.dnb.com/business-directory/company-profiles.government_of_the_united_states.b7a10c3efed8e705e9ea6611ad971dbe.html

That does not however mean that it necessarily became that way in 1871.

The organic act of 1801 did however incorporate the city of Washington DC

The fact that the united states federal government has a DUNS d&b number shows that it is indeed incorporated.

https://www.dnb.com/business-directory/company-profiles.government_of_the_united_states.b7a10c3efed8e705e9ea6611ad971dbe.html

That does not however mean that it necessarily became that way in 1871.

The act of 1871 did however incorporate the city of Washington DC