William was born in New York in 1861. As a youngster and a young man, he earned money wandering the streets doing paintings upon request. At age 26, he moved west to San Francisco, conducting painting excursions throughout the northern part of the state and establishing his studio on Geary Street.

Along with his artist wife Mabel (1861-1921), they relocated to Los Angeles in the 1890's for a few years. They then moved to Santa Cruz where William initially painted murals. In 1904, the original Beach Casino and Santa Cruz Boardwalk was built. William set up his concessionaire shop and a forty year long career was born. He did paintings for tourists, still lifes, forest scenes, forest fire scenes, beach and marine scenes for the grand sum of $1.00. Often, he painted on redwood panels, a treasured feature for tourists who came to California in part to gaze at the giant trees in and around Santa Cruz. Mabel and William had an artist son, Sydney Lemos (1892-1944).