Memoir 1, Page 60, The Confederate Surrender

"On the 26th of May 1865 the last army of the 'so called Southern Confederacy' surrendered."

The date referenced here is the day that General Edmund Kirby Smith of the Trans-Mississippi theatre surrendered his army. Following Lee’s surrender on the 9th of April, Smith had continued to send raids into Missouri; however, by May 26, he realized the futility of continued resistance and surrendered the last official Confederate army. Despite this surrender, Confederate forces continued to trouble Union territories, including General and Cherokee Chief Stand Watie and his force of Native American soldiers in Oklahoma, and the Confederate commerce raider CSS Shenandoah in the Bering Sea near Alaska. Watie finally surrendered June 23, followed by the surrender of the Shenandoah on November 6. Andrew Johnson declared the war officially over on August 20, 1866.