Starting out its service at Keokuk, Iowa, the regiment was transferred to Missouri in June, where it joined the forces of Nathaniel Lyon at Boonville.
On August 2, two companies of the regiment were present at the Battle of Dug Springs, and the entire regiment was engaged at the Battle of Wilson's Creek on August 10, when Lyon launched a surprise attack against the combined camps of the Missouri State Guard and a Confederate States Army force.
At Wilson's Creek, the 1st Iowa fought on a prominence known as Bloody Hill, first on Lyon's left flank and then moving to another position to support the 1st Kansas Infantry Regiment.
[4] Most of the men enlisted out of a desire to put down a rebellion against the United States government, and not out of abolitionist sentiment.
[12] The regiment was ordered to head to Missouri and join the forces of Brigadier General Nathaniel Lyon on June 13.
[14] At the time they left Keokuk, the men were armed with antiquated flintlocks that had been converted to use the percussion cap system.
[18] Lyon's advance from Boonville to join forces with the southern prong of his offensive was delayed by logistical issues.
[29] Reaching Forsyth on July 22, the command drove off a small opposing force in a minor skirmish and then looted the town.
[36] Lyon, unaware that Price and McCulloch had joined forces, began an advance from Springfield on August 1, hoping to defeat in detail the Confederates and Missouri State Guardsmen.
[37] On August 2, a portion of Lyon's command routed some Missouri State Guard cavalry in the Battle of Dug Springs.
[46] As the federals moved out on the evening of August 9, the Iowans sang loudly on the march,[47] which made Lyon worried that the men would not fight well due to levity.
[48] Lyon's attack surprised the Confederate camp on the morning of August 10, bringing on the Battle of Wilson's Creek.
[50] While Lyon held Bloody Hill, Sigel was defeated by a Confederate and Missouri State Guard attack.
Lyon then began to lead the 2nd Kansas Infantry Regiment forward from a reserve role, but was shot dead.
[59] One member of the 1st Iowa estimated that the regiment had marched 620 miles (1,000 km) from the time they reached Renick to the arrival at Rolla.
[61] According to Dyer, the 1st Iowa had 20 men killed in action or mortally wounded during its existence, with another eight dying of natural causes.
[8] At least 600 veterans of the regiment reenlisted in other units, and two, Francis J. Herron and Charles L. Matthies became general officers during the war.