Pacific Division of the U. S. Army was one of its superior administrative organizations that existed during the early 19th century and for a short time in the early 20th century.
The first Pacific Division of the U.S. Army was created on October 10, 1848, as the Army reorganized its administration for the new territories acquired during the Mexican–American War. 10th Military Department (California) and 11th Military Department (Oregon Territory) were subordinated to the new Division that had its headquarters at Monterey. In June 1849 division headquarters moved to the California, for a month then moved to Benicia and the Benicia Arsenal in the upper San Francisco Bay in July 1849.
On May 17, 1851, the Army merged Military Departments 10 and 11 into the Pacific Division as the Army again reorganized its administration on the West Coast. Both of those military departments merged into the Pacific Division ceased to exist. Division headquarters directly administered affairs in California and Oregon Territory. On June 15, 1852, Pacific Division headquarters was moved from Benicia to the San Francisco.
On October 31, 1853, the Pacific Division was replaced by the Department of the Pacific, with headquarters at San Francisco. It was created when the Army abandoned the system of divisions and numbered departments, establishing departments having a descriptive name, and reporting directly to Army Headquarters.
The Departments where again organized under new Divisions in 1904, with the Pacific Division having subordiate to it the Department of California and its subordinate District of Hawaii and the Department of the Columbia. The Division echelon was eliminated in 1907, as was the Pacific Division.