During the Black Hawk War, Abraham Lincoln of New Salem, Illinois served three enlistments. Each enrollment lasted for approximately 30 days.

His first enlistment was as elected captain of a company in the 4th Regiment of Mounted Volunteers, of Gen. Samuel Whiteside's Brigade. Lincoln enrolled on April 21, 1832, and mustered out with his company at Fort Johnson (Ottawa) on May 27, 1832. The company served at Beardstown, and reportedly Lincoln's company helped bury the dead of "Stillman's Run"— although this occurrence is still under investigation. Along with the muster-out of Lincoln’s company was the general muster-out of what became known as the “First Army” of Illinois. While a new army was being raised and organized, Illinois enlisted and mustered in a 20-day interim regiment (the so-called “Second Army”) and the only defense the State of Illinois had until the so-called “Third Army” could be brought into the field.

Lincoln re-enlisted on the same day he mustered out of his old company, and was mustered in on May 29 as a private in Captain Elijah Ises' Company, Twenty-Day Interim Regiment. He actively served with the company when General Henry Atkinson detached Captain Iles' command to ride north from Ottawa along the Kellogg Trail and reopen communications with Galena-- which had been out of touch with the rest of the world since the Felix St. Vrain Massacre. As part of this movement, Iles’ company (including Lincoln) spent an overnight at Apple River Fort... about a week before Black Hawk's attack against that strongpoint later in June. Once this ride was completed, the service of Iles’ company was essentially at an end. On June 16, Lincoln was mustered out.

Lincoln's third enlistment was as a private in Captain Jacob M. Early's "Spy Company." This unit mustered in approximately June 20, 1832, and served as part of General Atkinson’s army as it moved north through present-day Beloit, Janesvilles, the Storr's Lake encampment (west of present-day Milton, Rock County, Wisconsin) and on to the “Trembling Lands” east of present-day Fort Atkinson, Jefferson County, Wisconsin. Atkinson's food supply dwindled, and his solution was to muster out most of his militia. Accordingly, Early's company (along with Lincoln) was mustered out and discharged on July 10, 1832 near present-day Coldspring, Jefferson County, Wisconsin. The story goes that Lincoln had his horse stolen, so he and companion George Harrison (not the Beatle) reportedly walked and canoed several hundred miles back to New Salem.