He was elected lieutenant colonel of the First Regiment, Texas Mounted Riflemen in June 1846 and fought in the Battle of Monterrey in September. On October 2, 1846, Walker mustered out of federal service and headed for Washington D.C. to begin recruiting for his army. Following his arrival in Veracruz, Mexico, he was detailed to the First Pennsylvania Volunteers on May 27, 1847, who were stationed at Castle San Carlos de Perote to counter activities by Mexican guerillas between Perote and Jalapa. A few months later, Walker departed Perote along with Gen. Joseph P. Lane to guide a train transporting supply materials to Mexico City. However, Gen. Lane was informed of an enemy force of considerable size at Humantla and ordered that an attack be carried out. Walker’s mounted rifles took the lead, and the assault force arrived in Humantla on October 9. During the resulting battle with the Mexican army, Walker was shot and killed either via a shot in the back, or a man a infantry man carrying a lance. Walker was originally buried at Hacienda Tamaris, but in 1848, his remains were moved to San Antonio. On April 21, 1856, as a part of the Battle of San Jacinto celebration, he was reburied in the Odd Fellows’ Cemetery in San