Abraham Johnston who died in 1824 in Amwell, Washington County, PA. He is listed as Abraham Johnson on the 1781 tax list for Amwell and he registered his land in 1785 in the newly formed Washington County, PA. He had a number of sons; Abraham Jr., Robert, William, Samuel and Isaac. He had either a son or brother named John Johnston who lived near him in the 1790 and 1800 censuses. I think he had a few daughters as well.
Isaac died in Meigs County, Ohio in 1849. It looks like Isaac's son Asa died between 1846 and 1850. Asa had two sons and two daughters. His son Reuben and his brother Selden came to Minnesota.