Since Washington, DC is a reciprocal “state”, if you have
Maryland taxes withheld from your W-2, then you have no need to file a
Washington DC tax return.
If you have no need to file a return other than Maryland,
then you do not have to indicate you worked in another state.
Reciprocal states treat income as earned in the state you
live in.
Please take a look at the link below for further
information.
https://ttlc.intuit.com/questions/1899178-what-is-a-state-reciprocal-agreement