Looking on the internet deeply has found these results:

on August is the most popular phrase on the web.

in August 17,140,000 results on the web	on August 1231,000,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Light in August is a 1932 novel by the Southern American author William ..... .in August in Mississippi there's a few days somewhere about the middle of the�... Published in 1932, William Faulkner's Light in August chronicles the life and death of Joe Christmas, a man of ambiguous racial ancestry. Like The Sound and �... Auctions in August 2015 has concluded. If you won an item, you will be contacted by a branch representative for payment and pick up. You may search and view�... Aug 25, 2005 ... Quite often, the temperatures soar in August. ... Hi! I think the correct preposition is "in August", when u aren't talking about a specific date.	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

in August

17,140,000 results on the web

on August

1231,000,000 results on the web

More popular!

Light in August is a 1932 novel by the Southern American author William ..... .in August in Mississippi there's a few days somewhere about the middle of the�...
Published in 1932, William Faulkner's Light in August chronicles the life and death of Joe Christmas, a man of ambiguous racial ancestry. Like The Sound and �...
Auctions in August 2015 has concluded. If you won an item, you will be contacted by a branch representative for payment and pick up. You may search and view�...
Aug 25, 2005 ... Quite often, the temperatures soar in August. ... Hi! I think the correct preposition is "in August", when u aren't talking about a specific date.

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.