The Battle of Wilson's Creek, also known as the Battle of Oak Hills, was the first major battle of the Trans-Mississippi Theater of the American Civil War. It was fought on August 10, 1861, near Springfield, Missouri.

The trans-Mississippi theater of the American Civil War was the scene of the major military operations west of the Mississippi River. The area is often thought of as excluding the states and territories bordering the Pacific Ocean, which formed the Pacific coast theater of the American Civil War (1861–1865).