When I see a document refer to something going on in “London, England,” or “Detroit, Mich.,” I’m never sure if adding “England” and “Mich.” is a result of the writer’s ignorance (they don’t realize everyone knows where these places are) or arrogance (they know where these places are but assume others don’t) or just some misplaced duty to being complete. But many cities in the U.S., as well as around the world, do not require the larger locations appended to them and, in fact, look pretty silly when they are. Yes, there’s Paris, France, and Paris, Texas, and Philadelphia, Penn., and Philadelphia, Miss., so use common sense. If you have an event in Cairo, Ill., by all means be specific!
The AP Stylebook recently updated its list of cities in the U.S. and globally that stand alone, which is determined by the population of the city and metropolitan region, the frequency of the city's appearance in the news, the uniqueness of its name, and the chance that it’s almost synonymous with the state or nation where it’s located (when you hear Paris, do you think of Texas?).
In the U.S. these cities are:
Here are those cities around the world. I’ve added an asterisk to those newly added.