I am researching the Tompkins family that you referenced in your post and was wondering if you were able to connect 'your' Isael Tompkins to them yet?
"John Churchill wrote in his "Landmarks of Oswego County, N.
Y.," on page 523, that: "William H. Tompkins b. Saratoga Co., N.Y., January 1823, settled in 1835 at Granby, Oswego Co., N.Y. He had spent some time living in Onondaga Co. before reaching Granby. He came with his father, Benjamin, two brothers, Israel and Charles, plus a sister Phebe. They settled on lot 17 by the river. Benjamin died in 1858. According to the 1880 Census for Granby, Wm. H. Tompkins,
farmer, Age 57, with wife, Harriet, age 57, b. England, and daughter, Hattie E., age 17."