That is true. But many who live there are from somewhere else - more so as you get closer to DC and Baltimore. The counties that have more native Marylanders are less whacky, some even conservative. Case in point:
Andrew P. Harris (R), 1st Congressional District, MD, includes Cecil, Kent, Queen Anne’s, Caroline, Talbot, Dorchester, Wicomico, Worcester & Somerset counties & parts of Baltimore, Carroll & Harford counties. Most of those counties are well away from DC and Baltimore (most on the eastern shore). Even the portion in Baltimore county is the northern part, the most distant from Baltimore. Most of the counties in the district also went Republican in the last presidential election.
http://www.mdp.state.md.us/pdf/redistricting/2010maps/cong/dist_1.pdf