When addresses and place names appear in text, use commas to separate the individual elements. Think of it this way: at any point where you would start a new line when addressing an envelope, use a comma (so don’t set off abbreviations such as NE or zip codes with commas):
When touring the nation’s capital, make sure to schedule a visit to the White House, located at 1600 Pennsylvania Avenue NW, Washington, DC 20500, preferably in early April when the Japanese Cherry Blossoms are blooming.
When Jeff and I vacationed in Washington a few years ago, we rented a car and drove to Baltimore, Maryland, to watch the Vikings play the Ravens.
It can get awkward when you’re using a place name that requires a comma as an adjective:
This weekend, the Vikings played the Baltimore, Maryland, Ravens and beat them in a close game.
Your best bet is to rewrite the sentence to avoid the issue:
This weekend, the Vikings played the Baltimore Ravens and beat them in a close game.
This weekend, the Vikings played the Ravens from Baltimore, Maryland, and beat them in a close game.
Do you have a question about the comma? Let me know, and I’ll include it in a future installment of Mots Justes’ ongoing series.
The Mots Justes Series on Commas
Chicago Manual of Style, The. 15th ed. Chicago: The University of Chicago Press, 2003.
Hacker, Diana, The Bedford Handbook for Writers, 3rd ed. Boston: St. Martin’s Press: 1991.