Irvin McDowell
The courthouse first came under the control of Northern troops a month later as Union General Irvin McDowell began moving his 37,000 man army west toward Manassas on July 18, 1861. Manassas would become the site of the first major battle of the war. By the spring of 1862 the courthouse had ceased to function as a center for legal business and was simply used as a military outpost.