William Wallace Mills, El Paso pioneer, second son of James P. and Sarah (Kenworthy) Mills, was born at Thorntown, Indiana, on February 10, 1836. He received his early schooling there, and although he later was appointed to West Point, he never attended. In December 1858 he followed his brother Anson Mills to the town of Franklin, which Anson later renamed El Paso. Shortly after the election of Abraham Lincoln in late 1860, eight Southern states, including Texas, adopted ordinances of secession. In El Paso the Anglo-Americans were almost unanimously pro-Southern, and at a local election on the question of secession, there were less than a half dozen opposition votes. Two of these were the Mills brothers. Anson left for Washington, D.C., to serve the Union cause and later became a brigadier general; his brother went to New Mexico to join Union forces there. After Confederate forces occupied Fort Bliss in 1861, on one occasion they caught W. W. Mills in El Paso del Norte across the river and took him prisoner. He eventually escaped to New Mexico but never forgot or forgave Simeon Hart, whom he held responsible for his humiliation. With the restoration of Union control over New Mexico and El Paso in 1862 Mills, who had been named United States collector of customs at El Paso, gave full support to the federal district court at Mesilla, New Mexico, in the enforcement of the congressional law of July 1862, which provided for the confiscation of property of any person who had aided rebellion against the United States. The law thus offered Mills an opportunity to settle an old score with Hart, whose property was seized. The long struggle lasted for more than a decade, and even though Hart received a presidential pardon, it was not until 1873 that he finally recovered his property.
During Reconstruction Mills assumed the leadership of the local Republican party and formed the "customhouse ring," a vehicle for extending favors to local merchants, controlling appointments to office, and manipulating elections. By 1868 the dominant radical wing of the Republican party in Texas was receiving strong opposition from those seeking a more moderate policy. Mills was named a delegate to the Constitutional Convention of 1868–69 in Austin, where the radical majority selected Edmund J. Davis as president. Mills supported the moderates, led by A. J. Hamilton, and as a diversionary attempt to weaken radical strength in the convention proposed to establish Montezuma Territory from El Paso County and Doña Ana County, New Mexico. The proposal was rejected by Hamilton, however, who concluded that a division of the state would strengthen Governor Davis's hand. Yet Mills continued to support Hamilton, whose daughter he married in early 1869. Meanwhile, in El Paso the Republican leadership devolved upon Albert J. Fountain, who gave his full support to the radical wing. The radical victory in the governor's race in 1869 brought Mills's removal from his post as collector of customs, thus sharply curtailing his local power and influence. By 1872 radical rule in Texas had run its course with the defeat of Governor Davis, and in El Paso the Republican party was in ruins, shattered by the Fountain-Mills feud. Mills's political career had come to an end, although he did serve as United States consul in Chihuahua from 1897 to 1907. His memoirs, Forty Years at El Paso, remain the most complete account of that city during its formative years. Mills and his wife, Mary, moved to Austin in 1910, where they spent their last years. Mills died on February 10, 1913.