The Mobile District was an administrative division of the Spanish colony of West Florida, which was claimed by the short-lived Republic of West Florida, established on September 23, 1810. Reuben Kemper led a small force in an attempt to capture Mobile from the Spanish on behalf of the new republic, but the expedition ended in failure.
When in 1810 the United States annexed the Baton Rouge District, which had been under the control of the unrecognized Republic of West Florida, the Mobile District remained under Spanish control. The Mobile District was declared by Congress to be annexed to the United States on May 14, 1812, immediately prior to the start of the War of 1812 with Great Britain, with whom Spain was allied.
Nearly a year later, a U.S. military force arrived in Mobile to formally accept the presiding Spanish commander's surrender. The Mobile District was incorporated into the Mississippi Territory. From that point, Spanish Florida was equivalent in its geography to today's Florida; however, it would be nearly another decade before Spain ceded Florida to the United States.