The below article by Thomas Fuller is an extensive look into the phrase.
Horace Greeley (February 3, 1811—November 29, 1872) was an American newspaper editor and politician.
Greeley was an agrarian and supported liberal policies towards settlers: one of his famous phrases was "Go West, young man".
"Go West, young man!"—An Elusive Slogan
It was the motto of nineteenth-century America, the watchword of Manifest Destiny: "Go West, young man!" Although it is commonly attributed to New York newspaper editor Horace Greeley, works of reference give the exhortation confusing and contradictory origins.1 One of our most familiar historical slogans surely deserves more careful documentation than it has yet received. To that end, I have thoroughly investigated the history of the phrase.
This article briefly describes one aspect of my research that may interest Indiana historians: the truth behind a widely held belief that the phrase was originally written by John Babson Lane Soule (1815—1891), an Indiana newspaper editor, in an editorial in the Terre Haute Daily Express in 1851.2 I have examined this assertion with some care and have concluded that it is a fiction dating in print to no earlier than 1890. Before that date, the primary-source historical record contains not a shred of evidence that Soule had anything to do with the phrase.