Melissa, I think I just found James H. and Rebecca (Ash) McPherson in 1880 - living in San Simeon, San Luis Obispo, CA. If they did go to Montgomery County, they must have moved on.
His parents, James Starkey and Elizabeth Johnson McPherson, are buried in Bowers Cemetery, between Alsey and Manchester, in Scott County, Illinois. The cemetery is beside the blacktop road leading between the two towns.
James S. McPherson, b. 28 Jan. 1796, d. 19 Oct. 1879
Elizabeth McPherson, b. 29 Jan. 1799, d. 19 Sept. 1846