The public libraries provide great resources and services to any resident that chooses to take advantage of them. Proof of residency is all that is required to obtain a library card. A library card is all one needs to use the resources and services offered through the public library.
The District of Columbia, Maryland, and Virginia offer reciprocity. This means if you prove residency in any one of these places, you may get a library card for the other. [eg. If you live in DC, you can go to Arlington, VA; show proof of residency in DC; and Arlington, VA will issue you a library card for the Arlington, VA County Public Libraries.]