210
- 21001 Aberdeen
- 21005 Aberdeen Proving Ground
- 21009 Abingdon
- 21010 Gunpowder
- 21012 Arnold
- 21013 Baldwin
- 21014 Bel Air
- 21015 Bel Air
- 21017 Belcamp
- 21028 Churchville
- 21029 Clarksville
- 21030 Cockeysville
- 21031 Hunt Valley
- 21032 Crownsville
- 21034 Darlington
- 21035 Davidsonville
- 21036 Dayton
- 21037 Edgewater
- 21040 Edgewood
- 21042 Ellicott City
- 21043 Ellicott City
- 21044 Columbia
- 21045 Columbia
- 21046 Columbia
- 21047 Fallston
- 21048 Finksburg
- 21050 Forest Hill
- 21051 Fork
- 21052 Fort Howard
- 21053 Freeland
- 21054 Gambrills
- 21056 Gibson Island
- 21057 Glen Arm
- 21060 Glen Burnie
- 21061 Glen Burnie
- 21071 Glyndon
- 21074 Hampstead
- 21075 Elkridge
- 21076 Hanover
- 21077 Harmans
- 21078 Havre De Grace
- 21082 Hydes
- 21084 Jarrettsville
- 21085 Joppa
- 21087 Kingsville
- 21090 Linthicum Heights
- 21093 Lutherville Timonium