Take notes and photocopy maps. Start a folder or binder of possible sites by county. This way you can plan a days hunt. If one site doesn't pan out, you have a backup site to goto. The nice thing about the Internet is that you can do your research anytime, at your convience.
Lets do a step by step search for possible sites using services on the Internet.
If you follow these steps, you should have a number of possible sites. As an example, I will look for churches in Clarion County Pennsylvania. Lets start by using the GNIS Site Finder to locate possible sites. Enter county interested in. The GNIS database contains 30 churches for Clarion County.