Robert Johnston immigrated to the United States from England in 1849. He joined the Chicago Board of Trade Battery of the Illinois Artillery, formerly known as Stokes Independent Battery of Light Artillery, on March 10, 1863. He mustered in as a private in Louisville, Kentucky, nine days later. He mustered out on June 30, 1885 in Chicago.
Johnston was a founding member of Riverside Post 118, California-Nevada Department of the Grand Army of the Republic. The post was founded May 1, 1866 with 31 charter members. Other charter members buried at Evergreen include Captain Charles T. Rice, Elmer W. Holmes, and J.H. Woodward. Other notable Evergreen residents who were early GAR members include Adam Alkire, C.C. Miller, David G. Mitchell, William B. Johnson, and Prince Edwards.
Johnston spent his years in Riverside farming and in 1889, is listed as sharing a residence with local horticulturist C. G. Hurd. He was a long-standing member of the Magnolia Avenue Presbyterian Church and in 1889, Reverend J. W. Dinsmore officiated at Johnston’s funeral.