A great many style guides address the question of whether or not to separate the month and year with a comma in phrases of the type "January[,] 2018"—and yet, to my surprise, a search of English Language & Usage for the terms "month year comma" yields only one question that seems to focus on precisely this point: Is there always a comma before and after a year in a sentence?
Unfortunately, that question was closed as duplicate back in 2014, even though the prior question that it supposedly duplicates (How to use AP Style commas after dates) does not ask about "month[,] date" constructions, and even though none of the answers posted in response to that question address the issue either.
But the "Is there always a comma before and after a year in a sentence?" question doesn’t show any research, which would probably lead to its being closed again for that reason if it were reopened as not being a true duplicate—so rather than try to rehabilitate it, I ask the question afresh (and in my own words) here:
In instances where only a month and a year appear as date indicators—such as "January[,] 2018"—is it more common in print publishing (that is, in ink-and-paper books and magazines, whose publishers tend to enforce in-house or third-party style guidelines) to include a comma after the month or to omit it? Are the relevant style guides evenly divided on this issue, or do they preponderantly favor one or the other option?
Best Answer
Bryan Garner, Garner's Modern American Usage, second edition (2003) has a useful entry on this matter:
Garner might also have mentioned The Associated Press Stylebook and Briefing on Media Law (2002):
and Words into Type, third edition (1974):
and The Oxford Guide to Style (2002):
On the other hand, a quick check of the December 11, 2017 issue of The New Yorker finds the magazine still hewing to the practice of including a comma in "month year" phrases. For instance, Jon Lee Anderson, "Accelerating Revolution,"uses it six times:
Conclusion
As with all issues involving punctuation style, the first question a writer should ask in, "What style guidelines am I obliged to satisfy?" If the answer is "None," the writer can decide whether to follow preponderant publishing-house usage or to follow personal preference (if the two do not coincide). And in the case of "month[,] year" punctuation, the preponderance of usage clearly supports the no-comma option.