George Alexander Hanlin was born on February 23, 1844, near Hanlin Station, Pennsylvania, to Alexander Hanlin and Margaret Gracey. His father was a farmer who owned $12,000 of real estate and $3,218 of personal property by 1860. Hanlin grew up and attended school in Hanover, Pennsylvania. He enlisted in the Union army on August 18, 1862, and mustered in as a private in the 140th Pennsylvania Infantry on September 4. The regiment took part in the Battle of Chancellorsville, the Battle of Gettysburg, the Overland Campaign, and the siege of Petersburg. He eventually earned a promotion to corporal, and he mustered out on May 31, 1865.
Hanlin moved to Clinton County, Missouri, after the war and worked as a farm laborer. By 1870, he owned $600 of personal property. He married Eliza Catherine Stephenson in Daviess County, Missouri, on May 16, 1877, and they had at least four children: Willard, born around 1878; Clarence, born around 1880; Elmer, born around 1884; and Gracey, born around 1885.
They moved to Sacrament0 Gulch, Colorado, around 1879, and Hanlin earned a living as a hotel keeper there. He applied for a federal pension in August 1890 and eventually secured one. They moved to Denver, Colorado, around 1886, and Hanlin worked in the coal and feed business. He was an active member of the local Grand Army of the Republic post. He died of heart disease in Denver on January 27, 1906.