Classifying Your State's Counties

[Del Tachi]

Urban (1) - Hinds
Suburban (2) - Madison, Rankin
Exurban (3) - DeSoto, Hancock, Pearl River
Small Town (19) - Alcorn, Bolivar, Coahoma, Forrest, Harrison, Jackson, Jones, Lafayette, Lamar, Lauderdale, Lee, Lincoln, Lowndes, Panola, Pike, Oktibbeha, Warren, Washington, Yazoo
Rural (57) - the rest of 'em

[Del Tachi]

Urban - Baltimore City, Montgomery, Prince George's

How are these anything other than D.C. suburbs?

Simple density a city does not make.

[Del Tachi]

Urban - Baltimore City, Montgomery, Prince George's

How are these anything other than D.C. suburbs?

Simple density a city does not make.

For the sake of the argument, I'll assume you've never been to either one. If you've been there, you'd know that much of those counties have an urban feel to them. They're nearly comparable to DC itself.

I actually lived in DC for 4 years.

PG and MontCo aren't "urban" because DC is the obvious anchor of the whole DMV region.  The whole metro area is centered around Downtown DC - it's the transit hub, has the highest daytime density, and the densest, most high-value amenities.  Von Thünen's rings and what not. 

While relatively small geographic areas like Downtown Silver Spring or Bethesda may offer comparable density, you're ignoring the historical development of these places as commuter towns unipolarly oriented toward DC.  You're also ignoring that most of Montgomery/PG is more like Olney or Bowie than DC.