Everyone agrees that countries confer citizenship. So I’m a citizen of the United States.
It gets trickier when you get to the city and state level. The Associated Press’s AP Stylebook specifically says that states do not confer citizenship, but Garner’s Modern American Usage says that in the United States you can use citizen or resident when referencing a state. Since Bryan Garner is a lawyer, I tend to think he knows what he’s talking about for this kind of stuff; so at least in the legal realm, it’s likely OK to call me a citizen of Nevada. Further, the Oxford English Dictionary shows that citizen has a long history of being used to refer to an inhabitant of a city or town.
Still, since the Associated Press specifically recommends against calling people citizens of cities or states, and The Chicago Manual of Style seems to agree, I’d still say that in regular writing, you should stick to using citizen for people in countries and resident for people in cities and states. I’m a citizen of the United States, but I’m a resident of Reno and Nevada.
One reason people may be confused is that we sometimes do talk in general about being a good citizen. That can mean doing something like voting in your city elections or picking up trash at a local park, but that’s a slightly different meaning for the word citizen.
Even though @BatCruRon5 didn’t ask about monarchies, I’ll add that in monarchies, citizens are also sometimes referred to as subjects. Being a subject means that you owe allegiance to the king or queen.
Garner, B. “citizen. A. And resident.” Garner’s Modern American Usage. Oxford: Oxford University Press, 2003, p. 153.
“citizen, resident, subjection, national, native.” AP Stylebook, online edition. http://www.apstylebook.com/online/?do=entry&id=570&src=AE (subscription required, accessed June 3, 2015).
“citizen; subject.” The Chicago Manual of Style Online, 5.220, Good usage versus common usage. http://www.chicagomanualofstyle.org/home.html (subscription required, accessed June 3, 2015).
“citizen, n. and adj.” Oxford English Dictionary, online edition. Oxford University Press. http://0-www.oed.com.innopac.library.unr.edu/view/Entry/33513 (subscription required, accessed June 3, 2015)
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