One of the only sites I am aware of that provides any sort of data on the number and types of religious adherents by county is at The Association of Religious Data Archives. The Association of Religion Data Archives (ARDA) strives to democratize access to the best data on religion. Founded as the American Religion Data Archive in 1997 and going online in 1998, the initial archive was targeted at researchers interested in American religion. The targeted audience and the data collection have both greatly expanded since 1998, now including American and international collections and developing features for educators, journalists, religious congregations, and researchers. Data included in the ARDA are submitted by the foremost religion scholars and research centers in the world.
The biggest issue with the ARDA at the moment is that their data is a decade old. While still great information, there is a need to see updated information on religiosity. Fortunately the ARDA does have plans, hopefully this Spring, to release new data on religious affiliations.
In the mean time here are links to Oneida County and Herkimer County 2000 religious data.
