Microsoft Word says there should be a comma there! (Will underline it if there is no comma there.)
So that is that unless you want to argue with Microsoft.
It still serves a purpose, because it helps the reader parse the sentence correctly on the first pass. Sure, you could figure it out, but if you misinterpreted it the first time, you’d have to go back to the beginning to make sense of it. I would still strongly recommend a comma there.
All the more reason no comma is necessary after the year unless it is necessary for some other reason. I do not agree with many of MS suggestions, including when to use “which” or “that” but that’s another subject.
I would have gone with “… which is another subject.”
MS would probably agree with you.
Some style guides say (no cite, just memory) that you need a comma after a phrase if the phrase conventionally contains a comma. The example in the OP is one, but also:
The murder occurred in Mobile, Ala., and the body was later moved across state lines.
You are free to do as you choose. But as with other rules that people don’t want to follow (e.g. using “fewer” rather than “less” to describe countable objects), you’re basically choosing to have a large number of people think you’re wrong to make some sort of point. You’re not going to be around to tell everyone who reads your words why you’re a special snowflake, the rule is bad, the first use of “your way” appeared in 16,419 BC, or whatever. They’re just going to think “he’s doing this wrong” and move on. It’s easier just to conform – grammar isn’t a great moral sin that requires strident opposition, it’s just a set of admittedly arbitrary rules that we’ve mostly agreed on at this point in time.
Be very careful of using newspapers as style guides. The quirks of short column widths cause them to make a number of stylistic, punctuation, vocabulary, and grammatical choices that are unique to that specific industry. Visual layout, avoiding “rivers” or wide spacing, column lengths and weird pagination, and similar concerns cause newspapers to almost always be a special case. Dropping anything even vaguely optional to save space and characters is much more common in newspaper text than in other formal writing forms.
The online version of the Charleston Post and Courier includes the comma after the year. If you have an example of it being omitted in the printed version, it is probably for the reasons TimeWinder describes.
Well, the, “the elections on November 7, 2017, are expected to have a large turnout”. The comma does not contribute to clarity, and I myself would not include it. I wouldn’t see any point, and I would think a style guide requiring it is unduly fussy.
(Though, in fairness, I wouldn’t use the month-day-year format in the first place.)
In addition the the date, I would not use the comma after a state or country. Unless it was the end of a phrase or clause of course.
Well why did you put two commas for the date?
You can just do “On 2nd January 2016 XYZ happened”, no comma needed.
It all depends
If you say “last wednesday, the 2nd January 2016, XYZ happened”
the commas surround the additional clause.
If you add a complete sentence instead, you surround it with hyphens
If you say “last wednesday - BTW that day was my birthday - XYZ happened”
But it does depend if you are writing it as a record of spoken words, or for an actor to read, or you might put it in ( ) if its really information or in a novel.
Wait! We had two Januaries this year?
This is a style issue analogous to the one in the OP that many people, and indeed, many online publications, don’t seem to know about, or don’t follow. (Although I suspect it is mostly through ignorance, not a concious choice, like Siam Sam seems to be making.)
That is, when mentioning a city/state or city/country combination, a comma follows that latter term. “The author was born in Baltimore, Maryland, in 1955.”
ISTM that in both this case and that of the OP, the reason for surrounding the items in question with commas is that they are appositives. They add extra (but syntactically inessential) information that clarifies the precedent.
I know of no style guides that support omitting the second comma in the city/state or city/country case, Sam. I hope you’ll reconsider. 
A year or state after a city is a descriptor. If you put a comma in front of it, you must put a comma after it.
“I went to Columbus, Ohio, on April 4, 2011, by train.”
Omitting the second comma results in the misuse of the first comma.
I’m sorry, but no.
Most style guides say you should do this. Some do not. If you are not following any style guide you can do whatever you want, though you should want to avoid confusion. There is no such thing as must in usage.
This is not style. It’s grammar. A comma has certain specific uses—including to separate items in a list, to set off clauses from each other, and to set off subordinate phrases and clauses and appositives. In the last case, the comma must be used in pairs (unless you hit up against the start or the end of the sentence).
So, if you are not denoting a list, or separating clauses, the comma must be in pairs, indicating that the enclosed material can be lifted out without changing the meaning of the sentence.
If you use the comma this way —
“I went to Columbus, Ohio by train.”
Then you are indicating that there are two clauses that are separated by a comma.
“I went to Columbus” and “Ohio by train.”
But clearly this is nonsense. There is no valid use of a comma that accounts for this. The only way to write this sentence is with a second comma—
“I went to Columbus, Ohio, by train.”
This indicates that the portion set off by commas can be removed without changing the meaning —
“I went to Columbus by train.”
This is not a matter of style. Without the second comma, the punctuation is wrong.
A comma indicates a pause. Since if I were speaking “On the 8th day of January 1995 I wrote a letter”, I would say it this way, “On the 8th day of January, 1995, I wrote a letter”, that’s the way I would write it.
It’s a lot like “Thanks, John”, not “Thanks John”. The comma reflects speech patterns and the phrase doesn’t scan correctly without it.
It can indicate a pause, but very often does not. It’s very often used to set off appositives, introductory phrases, to separate clauses, etc., in which a pause may or may not be used in speech. For example, there is no pause in something like “I live in Chicago, Illinois.” And different speakers pause in different places, so it’s not at all a reliable way of figuring out where a comma belongs or not.
No. No! This is sheer madness. You do not need a comma after the state, it’s purely optional. I’ll not reconsider it, not even if you put a gun to my head.
Punctuation is not part of grammar. Languages were written for thousands of years before punctuation was invented. Heck, before spaces were invented. Ancient inscriptions show letter (or ideograph or hieroglyph) after letter without any additional means of distinguishing words, pauses, stops, or questions. Punctuation came in slowly over long periods of time, and various times and people and settings varied in their use. Historians can use these variations to help date old documents.
The one punctuation form that most people have heard of is the controversy over the serial (or Oxford) comma. Some people would put a comma after “stops” in that last paragraph; some people would not. That’s obviously comparable to the comma uses you say are mandatory. They are not mandatory. And they are not grammar. They are style or usage.
Even style guides are not mandatory. For my first book I was told I needed to conform to the Chicago Manual of Style. I went out and bought one. When I got the galleys I received an addendum: a list of about 50 in-house exceptions to Chicago style. Usage is no more law or mandatory than parents’ instructions to their own kids. You may get in trouble in their house if you don’t follow them, but you can’t expect the kids next door to do so.