He was one of ten children of Benjamin Johnson Sr. (ca. 1750-1828), a Revolutionary War soldier, and his wife who has not yet been identified.

Benjamin Jr. married Sarah Dashiell on November 26, 1799 near Salisbury, Maryland. They had ten children of whom two died in infancy: Margaret Handy, Joanna, John Dashiell, Samuel, Benjamin, William Purnell, Charles, and Elizabeth, who were all born in Maryland, and Samuel James, and Edward Killiam who were born in Indiana.

Benjamin was a Worcester County, Maryland milita captain beginning in 1808, and served in the War of 1812. He and his family and others from the Eastern Shore of Maryland emigrated to Dearborn County, Indiana in the spring of 1817. They probably crossed the Chesapeake Bay to Washington D.C., where an old family letter hints they might have attended the inauguration of James Monroe on March 20th. They then followed the Old National Road to Brownsville, PA where they embarked on flatboats and went down the Ohio River to Lawrenceburgh, Indiana.

Twenty-six years later, as an old man, he moved on with his wife and other family members to Jackson County, Iowa in 1843, where they farmed land southwest of Bellevue, IA. He reportedly asked to be buried under an old oak tree on a hilltop on his farm, and he rests there today, near the shade of a later descendant of that original oak.

Of his children: daughter Joanna ended up crossing the continent to California where she died; Benjamin was born afflicted, having an oversized head and was deaf and dumb; Samuel James had a law enforcement career in Washington D.C. where he was assistant doorkeeper of the U.S. House of Representatives and is buried in the Congressional Cemetery there; and Edward was a medical doctor.