William Stretch Abert (1 February 1836 – 25 August 1867) was an American officer in the Union Army during the American Civil War.
Abert was born on February 1, 1836 in Washington, D.C.. He was the son of Colonel John J. Abert, chief of topographical engineers of the US Army. William Abert was appointed lieutenant in the 4th U.S. Artillery in 1855. At the beginning of the Civil War Abert was promoted to captain and assigned to the 3rd U.S. Cavalry before serving as an aide to General George B. McClellan. He participated in the battles of the Peninsula Campaign in spring 1862. After the Battle of Antietam he was promoted to lieutenant-colonel of volunteers and joined the staff of General Nathaniel Banks. After being promoted to colonel, he was given command of the 3rd Massachusetts Heavy Artillery Regiment. He was brevetted to Brigadier on March 13, 1865 for "bravery and meritorious service during the war. After the war, he returned to the army and was promoted to major in June 1867 in the United States 7th U.S. Cavalry. Colonel Abert died on August 25, 1867 in Galveston, Texas and is buried in Rock Creek Cemetery in Washington, DC.