This article claims to have pinned down the date of Joseph Smith's supposed First Vision.
It hinges on the account of an axe stuck in a stump. Read it and ask the same question I did:
Is there any other reason for chopping wood in 1820 in March in upper New York state? Like– for a fireplace? For cooking food? Fence repair?
For more information, see The Mormon Mirage 3rd Edition: A Former Member Looks at the Mormon Church Today(Zondervan, 2009). Also available as an audiobook and as an expanded-text E-book for Nook, Kindle and other reading devices.