Day 133: Use a comma in dates when including the day.
This is easier to demonstrate than to explain, so here are the correct uses of the comma in dates.
“June 15, 2001” (This has a comma because it includes the day.)
“June 2001” (This has no comma.)
If you are using the format in example 1 as part of a larger sentence, you also need punctuation after the year.
“The explosion on June 15, 2001, was minor compared to the explosion on August 15, 2008.”