The 4th California Infantry was a volunteer infantry regiment recruited from Northern California during the American Civil War. It was organized in Sacramento, Placerville, and Auburn in September and October 1861.

The regiment was originally organized in 1861. Most of the recruits, caught up in war fever, expected to be sent to the eastern battlefields. They were disappointed to be instead ordered to garrison duty and related tasks on the West Coast, where they spent the remainder of their enlistments. The regiment served principally in the District of Oregon (Oregon and Washington Territory) and in the District of Southern California. However, some companies were shifted to Arizona later in the war. None of these duties required regimental strength, so the companies of the regiment were detached and scattered. The last elements of the regiment were mustered out on April 18, 1866.

The Regimental flag and Company B's flag were the only banners to survive the war and are preserved in the State Capitol. Other flags were taken from newspaper accounts. Most of the company flags were made by locals.