William Slack was born in Yorkshire, England, December 27, 1823. His parents were Richard and Ann (Britt) Slack, both natives of England. At the age of fourteen years, Mr. Slack was apprenticed to the trade of a molder, and after serving an apprenticeship of seven years, he followed that occupation as a journeyman until 1848

In that year he came to the United States, Landing in New Orleans. From there he went to Cincinnati, Ohio, and was employed as a foreman in the foundry of Baker & Morton. He held that important position until 1850. He then started overland for Utah. Locating at Salt Lake City, he turned his attention to the mineral resources of that territory, and in partnership with his brother-in-law, Richard Varley, opened iron and coalmines and built the first blast furnace established near Salt Lake. Not suited with the Mormon Community, he abandoned his enterprises there, and in 1852 came by the Southern route to California, and located at El Monte. There he rented land and established a dairy, and engaged in general farming, etc., until 1855. he then went to Ventura and Santa Barbara Counties, where he was occupied in stock-raising until 1859. In that year he moved to Texas and located at San Antonio. The breaking out of the war in 1861 rendered business enterprises so unsettled in that State that Mr. Slack returned to California and again took up his residence at El Monte. He was employed for several months as a superintendent in a distillery, after which he engaged in stock growing and farming upon disputed lands in the Temple Tract, south of town. The dispute over this tract of land was with Lucky Baldwin and developed into a lawsuit which was continued for a number of years, costing both parties a great amount of money. Regardless of the odds against him the legal battle ended finally in a victory for Mr. Slack, he being allowed to retain his land. In 1870 he went to the San Jose Valley, and for the next four years was engaged in the stock business, after which he returned to El Monte and purchased eighty Acres of land just south of town and entered into general farming. His lands were under a fine state of cultivation and very productive. He also purchased a residence and business building in El Monte, being for a time owner of the store occupied at the time by J.T. Haddox, pioneer merchant.

From 1881 to about 1885, he engaged in the butcher business conduction a meat market in El Monte. Mr. Slack was a liberal supporter of public enterprises. For a number of years he served as a trustee of the Lexington School District. He was a Democrat, and very conservative in his political actions.

Mr. Slack was thrice married. February 13, 1845, he wedded Miss Eliza Varley, a native of Yorkshire, England. She died at El Monte, December 29, 1879. They became the parents of the following named children: Elizabeth, William Thomas, Jonathan, Richard J., and Albert, all of whom are now deceased, and Eliza, Sarah Ann, Mrs. Mathews of Baldwin Park; Mary, Mrs. John Paterson, of Los Angeles; George of Redlands and Arthur V., of Huntington Park. In 1881, Mr. Slack married Mrs. Ann Montgomery, a native of England. Mr. and Mrs. Slack returned to England in 1885, and spent a year visiting the homes of their childhood and youth.

On their return from England they moved into a residence on Lexington Avenue, and there resided until the death of Mrs. Slack in 1891. In 1892 Mr. Lack was again married, his third wife being Catherine Ogden, a native of Ohio, whose parents were Zechariah and Mattie Hayden also natives of Ohio and early pioneers of San Diego.

No children were born to Mr. Slack except by the first marriage. Following the third marriage, Mr. Slack moved to Los Angeles, on Eastlake Avenue, where they resided for eighteen years. In 1911 they moved to Hollywood where they resided until death called Mrs. Slack in 1914 in her seventy-seventh year.

Fourteen months later, following a full and active life, and gratified in the satisfaction of having contributed his share to the upbuilding of the county he loved, Mr. Slack, at the age of ninety-two, answered the final summons. At his death he proudly claimed ninety-one direct descendents.