William Henry Jackson was born in Keeseville, New York, the eldest of seven siblings. His talents in photography and sketching were put to good use in the Vermont studios where he worked in his youth. With the advent of the Civil War, Jackson enlisted in the Union Army in 1862. In his diary, he notes that he was soon ‘…ordered to simply ‘sketch or draw’…anything [he] pleased’ by Colonel Asa P. Blunt. In addition to drawing camp life, one of his most valuable contributions to the Union war effort was creating maps to aid fellow soldiers in battle.
Jackson was honorably discharged in 1863 and returned home to studio work, friends, and his sweetheart Caddie Eastman. This comfortable life ended with the sudden annulment of their engagement in 1866. Fleeing his old life in Vermont, Jackson set out westward as a bullwhacker on the Oregon Trail. In his 1929 autobiography, Jackson notes, "I had to get away from those memory-filled scenes; but I had no idea that this misfortune was to send me to such far-away paths of adventure.”
Many sketches from this period were done at the end of 1866, when he worked at the Birch Farm near Salt Lake City. During the first half of 1867, Jackson left for California by wagon train. He wandered by foot about 100 miles from Los Angeles northward and back before hiring on as a vaquero driving horses to Omaha. In Omaha, he founded the Jackson Brothers Photography studio with his brother Ed and friends Arundel Hull and Fred Johnson. In 1869 Jackson married Mollie Greer, who died during childbirth in 1872. In 1873 he married Emily Painter, with whom he had three children: Clarence, Louise, and Hallie.