This diary documents the sights and sounds of the beginning of the Mexican War, as observed by young Rankin Dilworth, an officer recently graduated from the United States Military Academy. Dilworth's first entry of April 28, 1846, is from the garrison at Jefferson Barracks; his last entry of September 19, 1846, is from Monterrey, Mexico. As a member of Zachary Taylor's Army, Dilworth led his company of the 1st Infantry in an attack on the fortresses scattered along the eastern side of the city. Dilworth documented his transit down the Mississippi River to New Orleans, his travel by Gulf steamer to Brazos Santiago, and the long, hot trek overland to Monterrey. In the attack of September 23, 1846, on the eastern side of Monterrey, Dilworth was mortally wounded by a cannonball, but lingered on in agony just long enough to learn the American forces had captured Monterrey. He died on September 27, 1846. The diary contains his observations of the Mexican cities of Matamoros, Reynosa, Camargo, and Cerralvo, and how they appeared in 1846.