Jonathan Brockenbrough Beckwith was born in Virginia in June of 1800. His paternal great-grandfather, Sir Marmaduke Beckwith, a baronet, settled in Virginia in 1748 and became a merchant. His parents, Marmaduke Brockenbrough Beckwith and Rebecca Beckwith, cousins, were both born in Richmond. They were married in 1795. Jonathan Beckwith was their second son, younger brother to Francis Marion.

Sometime between 1830 and 1835, Beckwith married Margaret (Margarette) Dawkins (1802-1855), also a Virginia native. They had four children: Francis William (1836-1884), John B (b. 1840?), Roma Rebecca (1843-1924), and Roxa (sometimes Rosa) Ellen (1846-1927). Beckwith was a farmer in Parkersburg, Virginia (later Parkersburg, Wood County, West Virginia). In one of his letters, he also refers to having spent three years in a clerk's office, though he does not say during what part of his life. He is listed as an enslaver in 1850 and although he does not appear on the "1860 Federal Census Slave Schedules", his letters reveal clear Confederate bias and a dislike for the "abolitionists and their allies here the union men as they call themselves."

In 1863, a portion of land in Parkersburg reportedly belonging to Jonathan B. Beckwith (although it may have been the possession of his brother or the extended Beckwith family in the region) was confiscated by the US government during the American Civil War. The land was noted to be the property of someone "of doubtful loyalty to the Union," which makes this Beckwith the likely owner. Construction began on Fort Boreman in May. Beckwith's younger son, John, served in Company E ("Border Rangers"), 8th Virginia Cavalry of the Confederate army as a private, then sergeant. Conflicting sources report he was either killed in action during the battle of Fisher's Hill, September 22, 1864 or he survived the war and died in Wood County, West Virginia at a later date.

Following the Civil War, the Beckwith family did reclaim the property that housed Fort Boreman. Jonathan B. Beckwith faced a number of lawsuits and railed against West Virginia and the local government in an 1866 letter. Although he professes a desire to sell his land and leave (if not for the legal predicaments), he remained in Wood County for the rest of his life. He died in 1891.

The identity of the recipient of both letters is uncertain, as Jennings was a family name among several generations of Beckwiths. Since Beckwith addresses the second letter to "Uncle," the most likely candidate is his father's brother Jennings. Little information, however, is available on this particular Jennings Beckwith, other than his parentage. His parents (and therefore Jonathan B. Beckwith's paternal grandparents) were Marmaduke (1734-1801) and Sybel (Sybil) (Ellzey or Elsie) Beckwith (1740-1825).