According to church conference reports, newspapers, church periodicals, presbytery records and published interviews from the 1820's, there was no revival between 1820 and 1821. Local churches recorded very few additions to their congregations in the early 1820's.
For example, in 1820, the Baptist Church in Palmyra only received 8 people through profession of faith and baptism, the Presbyterian church added 14 members, while the Methodist circuit lost 6 members, dropping from 677 in 1819 to 671 in 1820 and down to 622 in 1821 (see Geneva area Presbyterian Church Records, Presbyterian Historical Society, Philadelphia, PA; Records for the First Baptist Church in Palmyra, American Baptist Historical Society, Rochester, NY; Minutes of the [Methodist] annual Conference, Ontario Circuit, 1818-1821, pp. 312, 330, 346, 366).
In the Rise of Mormonism: 1816-1844 by Michael Marquardt, the author reviews several of the local church records and come to the same conclusion as that of the reference above.
There are a few apologetics who seem to think that the lack of information regarding the 1820 revival is due to the fact that it was so common that it was not deemed newsworthy. Of course this is grasping at straws. Church membership is a big deal to Church's and they tend to keep fairly good records, although sometimes those records are lost as is the case with many of the records of the local Palmyra denominations.
I agree that this point may be insignificant in and of itself and most believing Mormons would not have a problem with it. My current questioning of the Church is not due to one huge lie that can be proved 100%, it has to do with the hundreds and thousands of inconsistencies that all add up. When coupling this information with recorded accounts from Church history and local history where these accounts took place, the overall picture results in a web of contradiction that can, in my mind, only conclude that the First Vision is a magnificent story strewn together by Joseph Smith.
Note: In the original draft I included references regarding Joseph Smith joining the Methodist church in 1828 which I subsequently removed due to insufficient and satisfactory proof that he did so.
The Rise of Mormonism: 1816-1844 By H. Michael Marquardt