 Willis was born on January 9, 1831 in New York City and when he was nineteen he traveled west for the California Gold Rush.On August 24, 1861 he mustered into the service of the Union Army, becoming a first lieutenant and later a captain of Company A, 1st California Infantry.From San Diego, Willis marched with James H. Carleton's expedition across New Mexico Territory and was involved in the capture of Tucson, an old Spanish presidio defended by a handful of militia.