Captain James Allen (1806-1846) graduated from West Point in the same year as Robert E. Lee. Trained as an engineer, Allen was posted at Sault Ste. Marie in Michigan Territory. In 1832, he was part of an expedition along the upper reaches of the Mississippi River. Attached to the First Dragoons, he saw duty throughout the west, from St. Louis to Chicago to Fort Leavenworth. In 1842, he was posted in Iowa, Captain of Company I. In 1843, he established and commanded Fort Des Moines. The following year, he set out to explore north and west.
The details of his 2-month expedition (August to October 1844) are available here. Often, such documents are mostly an account of daily tasks, the lay of the land, notable flora and fauna, and the occasional bit of excitement. This one certainly has most of these but lacks the excitement. Indeed, the most exciting parts are when the men are stuck in the mud during a heavy rain or one of the wagons breakdown. On several occasions, the column - Allen's command consisted of approximately 70 men - encountered Souix warriors, but nothing came of it. The Souix monitored the soldiers but there were no hostilities. Allen's account was submitted to the House of Representatives in March of 1846.
There are multiple maps and even an additional account of the expedition from an anonymous soldier in his command. Having lived in Iowa for many years, it is interesting to see it as a wilderness to be explored.
In 1844, Joseph Smith - founder of the Mormon Religion - was murdered in Illinois and his followers fled. Many were encamped in Iowa with plans to migrate further west. In 1846, the United States declared war on Mexico. Troops were needed. Captain James Allen recruited 500 Mormons from among those in Iowa; thus the Mormon Battalion was formed. The battalion set out from Council Bluffs, Iowa, to rendezvous with the Army of the West in Fort Leavenworth, Kansas. N.B. Neither Iowa nor Kansas were states yet. Lt. Col. Allen fell ill and was unable to depart with his troops, remaining at Fort Leavenworth with the intention of catching up later. He died on August 23, 1846.
Iowa became the 29th State on December 28, 1846.