Technically, "people," "peoples," and "persons" have different meanings. Here's an overview which one you should use.
Believe it or not, in the 1800s and early 1900s, many people objected to the use of “people” as I just used it. You weren’t supposed to write about “many people,” or “100 people” or so on. “Many persons” and “100 persons” was the right way to say it. Or at least there was a big debate at the time, with many people (persons?) arguing that “persons” was better, even though people had been using “people” all the way back in Chaucer’s time.
Merriam-Webster’s Dictionary of English Usage doesn’t record any reason for the debate; people just argued and debated about it.
Use 'people,' not 'persons'
Thankfully, those days are over, but the change was still quite recent. The AP Stylebook, for example, updated its entry to recommend “people” instead of “persons” sometime around 1980, according to the MWDEU.
Nowadays, “people” is almost always the right choice when you are talking about more than one person.
“Persons” is rare, and the dictionaries that do include it often note that it is uncommon, archaic, or going out of style; although, it does still appear in legal writing, which is often more slow to change than general writing, and it appears in set phrases such as “missing persons.”
So the bottom line is that unless you’re writing legal documents, you’re using set phrases such as “persons of interest,” or you’re writing fiction and you want your characters to sound like they’re in the 1800s or early-to-mid-1900s, use “people.”
But now we have one more word to consider.
'Peoples' has a specific meaning
After a recent segment about “monies,” a plural of “money,” a listener named Alan commented that he didn’t like “monies” and also said as an aside that he didn’t like “peoples” either. So what’s up with “peoples”?
I’m not talking about the possessive, like “The People’s Court.” I’m talking about a second plural form, as in “peoples of the Andes” or “Indigenous Peoples Day,” a holiday that is sometimes observed instead of Columbus Day in the United States (and is sometimes written without an apostrophe).
Of course, “people” is already the plural of “person,” but “peoples” is another term for a race, group, or nationality; and both the AP Stylebook and The Chicago Manual of Style acknowledge “peoples” used in this way.
This use isn’t new. The Oxford English Dictionary has examples of “peoples” going back to the Wycliff Bible in 1382 and Chaucer in 1425.
In general today, “peoples” is used to write about more than one group. For example, you can write about the American people — that’s one group — but if you were writing about people who speak English, and you wanted to emphasize that this one big group is actually made up of many smaller, distinct groups, you might write about “English-speaking peoples” instead of just “English-speaking people.”
Interestingly, this distinction somewhat parallels how we use the odd plural “monies,” in that finance writers tend to use “monies” to talk about a pool of money that has come from multiple sources. For example, maybe there are 20 different groups that make up English-speaking peoples, and maybe there are 20 different grants that combine to make a pool of monies.
Read More: ‘Monies’ vs. ‘Money’
I’m with Alan in that I don’t love the words “monies” or “peoples,” mostly because they draw too much attention to themselves, but they aren’t wrong, and they do have specific meanings, and if you want to draw attention to that meaning, then they are an excellent choice. Just don’t use them when you simply mean “money” or “people.” They aren’t just fancy plurals for those words.