Robert McKinney was born on January 26, 1819, in Ireland, to James and Sarah McKinney. He married Mary Jane Smythe, and they had at least five children: William, born around 1845; Sarah, born around 1847; James, born around 1848; Robert, born around 1852; and Mary, born around 1854. He immigrated to America by the early 1840s and settled in Troy, New York. He worked as a machinist. He supported the Democratic Party and named one of his children after President James K. Polk. The family moved to Cincinnati, Ohio, around 1861, and he died unexpectedly there on July 24, 1864.