According to the 1860 U.S. Census, California, a free state, had a population of 379,994.
According to The Union Army, "No quotas were assigned to the state under the several calls for troops during the war, though she was asked to furnish several regiments and battalions, aggregating more than 16,000 men, besides 500 who were enlisted within her borders and became part of the quota of the state of Massachusetts, and eight companies raised for Washington Territory. She furnished to the Union armies during the war two full regiments of cavalry, eight full regiments of infantry, one battalion of native California cavalry, and one battalion of infantry, called mountaineers, in addition to the above-mentioned companies of volunteers supplied to Massachusetts and Washington Territory. Altogether nearly 17,000 volunteers were enlisted in the state."
During the Civil War more than 16,000 Californians served in the Union forces, and, as a result, the state suffered nearly 600 soldiers in killed and hundreds more in wounded.
Due to its location, the state's local militia companies remained under state status because of the great number of Southern sympathizers, the Indian threat, and possible foreign attack. The state followed the usual military practice of mustering militia companies into regiments. These Volunteers maintained military posts vacated by the regular army units that were ordered east. However a number of state militias disbanded and went east. Several of these companies offered their services and were accepted by the Union Army.
Many of these men were stationed in California with the task to secure the borders from hostile American Indian tribes. Although a number of companies saw service on Eastern battlefields, they did not maintain their California designation. For example, the 1st California Regiment led by Abraham Lincoln's personal friend, Edward Baker, was later re-designated the 71st Pennsylvania. Beyond the battlefield, Californians contributed more than $15 million in gold, which the Lincoln administration used to shore up the economy during the war.
At the outbreak of the Civil War, Southern California secession seemed possible; the populace was largely in favor of it, militias with secessionist sympathies had been formed, and Bear Flags, the banner of the Bear Flag Revolt, had been flown for several months by secessionists in Los Angeles and San Bernardino counties. After word of the Battle of Fort Sumter reached California, there were public demonstrations by secessionists. However secession quickly became impossible when three companies of Federal cavalry were moved from Fort Mojave and Fort Tejon into Los Angeles in May and June 1861. Suspected by local Union authorities, General Johnston evaded arrest and joined the Los Angeles Mounted Rifles as a private, leaving Warner's Ranch May 27 in their journey across the southwestern deserts to Texas, crossing the Colorado River into the Confederate Territory of Arizona, on July 4, 1861. The Los Angeles Mounted Rifles disbanded and members joined the Confederate Army when they reached the Arizona Territorial capital of Mesilla (now in New Mexico). Like other pro-Confederates leaving California for the Confederacy, the volunteers joined up principally with Texas regiments. General Johnston joined the fight in the east as a general with the Confederacy and was later killed leading their army at the Battle of Shiloh.
The only Confederate flag captured in California during the Civil War took place on July 4, 1861, in Sacramento. During Independence Day celebrations, secessionist Major J. P. Gillis celebrated the independence of the United States from Britain as well as the Southern states from the Union. He unfurled a Confederate flag of his own design and proceeded to march down the street to both the applause and jeers of onlookers. Jack Biderman and Curtis Clark, enraged by Gillis' actions, accosted him and "captured" the flag. The flag itself is based on the first Confederate flag, the Stars and Bars. However, the canton contains seventeen stars rather than the Confederate's seven. Because the flag was captured by Jack Biderman, it is often also referred to as the "Biderman Flag". Continue to California in the Civil War.