The Battle of Moore's Mill was an American Civil War battle that took place in Central Missouri on July 28, 1862 along Auxvasse Creek near modern-day Calwood. This engagement, the Battle of Kirksville a week later, and the Battle of Compton's Ferry would drive the main Southern recruiters from northern Missouri. The Moore's Mill Battlefield was added to the National Register of Historic Places in 2015.

Following the Battle of Pea Ridge, Arkansas and the resulting Confederate withdrawal from northern Arkansas, recruiters were dispatched throughout Missouri in an attempt to rebuild the Confederate forces. Southern guerrillas aided the recruiters and often fought alongside them.

Guerrilla warfare plagued Missouri from the start of the conflict in Missouri, but intensified in early 1862 as the weather warmed. To combat the growing guerrilla menace General Henry W. Halleck issued General Order Number 2 on March 13, by which Missourians were "warned that if they join any guerrilla band they will not, if captured, be treated as ordinary prisoners of war, but will be hung as robbers and murderers". Confederate President Jefferson Davis responded on April 21, 1862 attempting to legitimize guerrilla warfare by authorizing commissions for those forming bands of "partisan rangers". but this was not accepted by the United States authorities. On May 29 Brigadier General John Schofield responded with General Order No. 18 to the Missouri State Militia which read in part:

When caught in arms, engaged in their unlawful warfare, they will be shot down upon the spot.

As guerrilla warfare and recruiting increased, and as the state had been stripped of nearly all but the new volunteer Missouri State Militia Cavalry regiments, guerrilla action and Confederate recruiting began to press Missouri harder throughout the summer. The Missouri State Militia commanders and Union Volunteers began to converge on Joseph C. Porter's recruiters and associated guerrillas, fighting small action at Vassar Hill on July 19, Florida on July 22, and Santa Fe on July 24.

Meanwhile, on July 22 General Schofield with the aid of Missouri's provisional Governor Hamilton Rowan Gamble ordered a compulsory militia enrollment, the Enrolled Missouri Militia, in an effort to raise a sufficient body of men for community defense. Schofield issued General Orders No. 19 requiring all able bodied loyal men to enroll in the militia and the disloyal to register stating their sympathies.

While these orders did raise a militia force for garrison duty and local policing that freed the Missouri State Militia for active pursuit of guerrillas and recruiters, the policies also forced those of Southern loyalties to choose sides. Thousands chose the brush, guerrilla bands, or to seek out recruiters to join the Southern army. Joseph C. Porter and John A. Poindexter's Confederate recruiting commands would immediately benefit from the order as Southern sympathizer flocked to their banners. In the meantime it would be several weeks before this newest Missouri militia would be ready to take the field.

In Jefferson City on July 27 Colonel Odon Guitar of the 9th Missouri State Militia Cavalry (9th MSM Cavalry) received instructions to reinforce Lieutenant-Colonel Shaffer in Columbia with two companies, which he did. Guitar also received intelligence that Porter and guerrilla leader Alvin Cobb were encamped together only 11 miles north of Fulton at Brown's Spring.