Union was founded in 1825 and became the second county seat of Franklin County, replacing New Port, which had served since the county separated from St. Louis County in 1818. In 1859, John T. Vitt built the brick structure at this site and opened a roller mill and later a sawmill. As the secession crisis deepened in early 1861, Franklin County citizens divided, militias formed, and men drilled for conflict. After debate at the old courthouse on February 22, 1861, the county chose a pro-union delegate to Missouri's state convention, which voted overwhelmingly against secession on March 19, 1861. Even so, tension continued as troops gathered in St. Louis to protect the city's large arsenal. On April 20, 1861, eight days after the firing on Fort Sumter, schoolteacher David Murphy assembled at least 50 Union men here and enrolled them in federal service before they moved to St. Louis. This group became the nucleus of Rifle Battalion Company A, First Missouri Infantry, the first force raised in out-state Missouri to join the defense of St. Louis. On October 1, 1864, Major General Sterling Price's Confederate army reached Union and confronted a small Franklin County Militia force that had fortified the mill and a bridge over the Bourbeuse River. Price, commanding an estimated 12,000 troops in a campaign aimed at St. Louis, had entered Missouri from Arkansas in mid-September. The fight began when elements of his army arrived from the direction of St. Clair that afternoon. Colonel Robert Lawther's 10th Missouri Cavalry forded the Bourbeuse to the east and cut the St. Louis Road north and east of the mill, while Confederate artillery fired from heights south of town. Many defenders escaped after Captain Henry Detmer ordered, "Everybody for himself." The number of Union casualties at Vitt's Mill remains disputed, though Confederate reports claimed as many as 100 killed, wounded, or captured. Afterward, Confederate troops used the mill to grind flour, occupied Union for several days, and consolidated there with forces arriving from St. Clair and Pacific before moving west in two wings toward Jefferson City, which they attacked on October 7.
