When to use a comma:
* After a city name:
* Example: "She lives in Denver, Colorado."
* When listing a city and state in a series:
* Example: "We visited Chicago, Illinois, and then drove to Nashville, Tennessee."
* When the state is used as an adjective:
* Example: "She has a California accent."
When to NOT use a comma:
* When the state is part of a proper noun:
* Example: "He lives in North Dakota."
* When the state is used as a possessive:
* Example: "The state's governor is a popular figure."
* When the state follows a ZIP code:
* Example: "Our address is 123 Main Street, Anytown, CA 91234."
Tip: If you're unsure, it's usually safe to err on the side of using a comma. It's always a good idea to double-check with a style guide or online grammar checker.