How do I track what religion a family practiced after leaving the family religion?

The Martins came over from England w/ the Quaker group who immigrated to Pennsylvania. They then migrated to NC, VA, KY, and then throughout the U.S. in the 20th century. At some point in the 1800s, they blended in w/ the religion of the local region where they were living. How do you go about accessing that information? The Canadian census listed "religion" but ours does not.
Answers

Hi, some churches do keep records of parish business and you pay to view them. I would check out the region where they lived and start looking for local history of the district, they usually mention churches etc. Perhaps if you checked out the library of that area, some provide online access to local history of the region. Maps of the time can also provide vital information.
If they were still active members in old age then maybe the death certificate will provide burial details.
Good luck