He was the son of James Denniston (ca. 1770–1825) and Prudence Morrison Denniston. On September 24, 1823, he married Julianna Howell (d. 1825). Afterwards he married Mary Scott, and they had five sons and six daughters.
^The name is given sometimes erroneously, especially in contemporaneous newspaper accounts, as Robert Dennison
^Salisbury Mills is a hamlet that lies partly in the towns of Blooming Grove and Cornwall. He died at the same place where he was born, in that part of the hamlet of Salisbury Mills which lies within the Town of Blooming Grove.