Barton Stone Alexander (September 4, 1819 – December 15, 1878) was an American engineer commander during the American Civil War who rose to the brevet rank of brigadier general in the regular army. He was a graduate of the U.S. Military Academy at West Point and served in the United States Army's Corps of Topographical Engineers, which at times was both a part of and separate from the United States Army Corps of Engineers. After graduating from West Point as a second lieutenant in the Class of 1842, he served in the Mexican-American War, building fortifications to protect American supply lines in the advance on Mexico City. After the end of the war, he was stationed in Washington, D.C., where he served as architect for the Scott Building and Quarters Buildings at the U.S. Soldiers' Home and took over the completion of the Smithsonian Institution Building after dissatisfaction with the pace of the first architect caused him to be dismissed.