[7] It is named after an Alabama plantation owner, Colonel William Johnson, who sowed its seeds on river-bottom farm land circa 1840.

[11] A genetic study employing microsatellite markers has investigated Johnsongrass populations across 12 US states and confirmed that the weed was introduced to US from Alabama and North Carolina.

After trans-continental railroad building the two founding populations began to intermix at around Texas shifting diversity from centers of introduction.

[12] The 1889 book The Useful Native Plants of Australia records that Sorghum halepense is a "strong, erect-growing species, varying from two to ten feet high, succulent when young, a splendid grass for a cattle run, though not much sought after by sheep.

The settlers on the banks of the Hawkesbury (New South Wales) look upon it as a recent importation, and seed of it has been distributed under the name of Panicum speciabile.