Griggstown is a regional area within Franklin Township, which is part of Somerset County. The Griggstown Reformed Church has a website: http://grchurch.org/
The church address is:

Griggstown Reformed Church
1065 Canal Rd
Princeton, NJ 08540
908-359-3604

By the way, don’t let the Princeton address fool you since it depends on which postal service is physically located closest to the address. The church is in Somerset County. You might contact the church directly or possibly get in touch with the Somerset County New Jersey GenWeb. The Somerset Historical Society may also be a resource for you. Griggstown is in a beautiful area. I used to go canoeing in the canal when I lived in Somerset County.

Millie Van Ness