Short answers, pulled from the story.
The Battle of Wilson's Creek was fought on the 10th of August 1861, about ten miles southwest of Springfield, Missouri. It was the first major battle of the Trans-Mississippi Theater of the American Civil War.
Brigadier General Nathaniel Lyon was killed at Wilson's Creek while personally leading a counterattack by the 2nd Kansas Infantry Regiment. He was the first Union general to die in battle during the Civil War. Confederate Colonel Richard Weightman also received a mortal wound in the same fighting.
Lyon commanded 5,431 men against an estimated 12,125 Confederate and allied troops, with no reinforcements available and many of his soldiers' enlistments expiring. His only other option was to withdraw to Rolla without fighting. Lyon was described as naturally aggressive and chose to attack rather than retreat.
A case of mistaken uniforms destroyed Sigel's position. The 3rd Louisiana Infantry approached wearing gray that matched the uniform of the 1st Iowa, a Union regiment, and Sigel's officers held their fire thinking the column was friendly. By the time the error was confirmed, four Union guns had been overrun and the brigade was routed.
Around 1,317 Union soldiers were killed, wounded, or captured at Wilson's Creek, against an estimated 1,222 Confederate, Missouri State Guard, and Arkansas casualties. Nearly a quarter of Lyon's entire force became casualties. The 1st Kansas's count of killed and mortally wounded ranked seventh-highest for any Union regiment in the entire war.
Five Union soldiers who fought at Wilson's Creek were awarded the Medal of Honor in the 1890s: Lorenzo Immell, John Schofield, Henry Clay Wood, William M. Wherry, and Nicholas Bouquet.