Maj. Gen. Samuel D. Sturgis, USA Brig. Gen. Ben McCulloch, CSA Lyon had an 'Army' of maybe 6,000; the Confederates had around 12,000.
The Union lost a bit over 1,300 men, the Confederates around 1,200. Brig. Gen. Nathaniel Lyon's Army of the West was camped at Springfield, Missouri, with Confederate troops under the commands of Brig. Gen. Ben McCulloch approaching. On August 9, both sides formulated plans to attack the other, McCulloch confident in superior numbers, Lyon as a pre-emptive attack. Lyon left about 1,000 men behind to guard his supplies, the Federal commander led 5,400 soldiers out of Springfield on the night of August 9. Lyon's plan called for 1,200 men under Colonel Franz Sigel to swing wide to the south, flanking the Confederate right, while the main body of troops struck from the north. Success hinged on the element of surprise. Ironically, the Confederate leaders also planned a surprise attack on the Federals, but rain on the night of the 9th caused McCulloch (now in overall command, although feuding with Price) to cancel the operation.
About 5:00 am on the morning of the 10th, Lyon's attack caught the Southerners off guard, driving them back. Forging rapidly ahead, the Federals overran several Confederate camps and occupied the crest of a ridge subsequently called "Bloody Hill." Rebel cavalry received the first blow and fell back away from Bloody Hill. Nearby, the Pulaski Arkansas Battery opened fire, checking the advance and allowing Confederate infantry time to form a new battle line on the hill's south slope. The Confederates attacked the Union forces three times that day, over five hours but failed to break through the Union line. On Bloody Hill at about 9:30 a.m., General Lyon, already twice wounded, was killed leading a countercharge and Maj. Samuel D. Sturgis replaced him. Meanwhile, after initial Union success, the Confederates had routed Sigel's column south of Skegg's Branch. Sigel's defeated men fled.
Following the third Confederate attack, which ended at 11:00 am, the Confederates paused. Sturgis realized, however, that his men were exhausted and his ammunition was low, so he ordered a retreat to Springfield. The Confederates were too disorganized and ill-equipped to pursue. This Confederate victory buoyed southern sympathizers in Missouri and served as a springboard for a bold thrust north that carried Price and his Missouri State Guard as far as Lexington.
In late October, a rump convention, convened by Governor Claiborne Fox Jackson, met in Neosho and passed an ordinance of secession. Wilson's Creek, the most significant 1861 battle in Missouri, gave the Confederates control of the southwestern quarter of Missouri, but that was their limit: the Union held the rest.