When actual war was declared on Mexico, Kentucky militiamen and 43,500 soldiers from other states readied themselves for the march to the front. Kentucky's quota of two infantry regiments and one cavalry regiment was raised within four days following the call for troops, and just 13 days after the declaration of War with Mexico. There, under the command of Zachary Taylor, they distinguished themselves in the Battle of Buena Vista and in the decisive defeat of Santa Ana's Army at Cerro Gordo. At Buena Vista Jefferson Davis' 1st Mississippi Rifles, the 2d Kentucky Rifles, the 2d and 3d Indiana, and the 3d Ohio volunteer regiments united in a supreme force.
Never had the salutary effects of combined discipline and leadership of American citizen-soldiers been more convincingly demonstrated than in that desperate two-day struggle. At the Battle of Cerro Gordo, Captain John Williams' cavalry company led the attack. This battle would win Williams his nickname, "Cerro Gordo" Williams. Kentuckians also fought at the Battle of Monterrey. Of further interest is the fact that Kentucky Militiaman such as Captain Cassius Clay, Major John C. Breckinridge, Lieutenant Colonel Thomas L. Crittenden, and Lieutenant Colonel Henry Clay, Jr. were all commanders in this War. Lieutenant Colonel Henry Clay Jr., was mortally wounded at the Battle of Buena Vista, he was carried off the field in the arms of a future Civil War General and Adjutant General, Frank L. Wolford. During the entire war, 4,694 Kentuckians served, of which 612 were casualties.