I am looking for a blueprint or floor plan and the designer who
copyrighted an exisiting home built in 1974 in Maryland. The address
is as follows: 9011 Longbow Road, Fort Washington, MD 20744. This
should be available to the public but I am uncertain how to further my
search for this specific house plan.

Blueprints are usually submitted to the local authority responsible
for issuing building permits, in order to obtain the permits.

In the case of Fort Washington, the responsible local authority is the
Prince George's County Department of Environmental Resources, Permit &
Review Division:

http://www.co.pg.md.us/Government/AgencyIndex/DER/permit.asp?h=20&s=40&n=70

On the above webpage, you will find contact information for the PRD.
Since the building you are interested in was constructed 30 years ago,
it is not possible to state with any certainty that they will be able
to provide you with the plans; however, if anyone has them, it would
be the PRD.

I have posted this initially as a Comment, because you will need to
contact the PRD yourself to find out if they actually have the plans
you are seeking. For many jurisdictions, you will actually need to
appear in person in order to see the plans, for security and privacy
(of the present residents) reasons.

If you find that this information has been helpful to you, please let
me know so that I may post this as an official Answer for you to
accept and rate.

Thanks,

aht-ga
Google Answers Researcher