William Willis Garth (October 28, 1828 – February 25, 1912) was an American politician. He served as a representative of the Alabama 6th Congressional District in the U.S. House of Representatives between 1877 and 1879.
Garth was born on October 28, 1828 in Morgan County, Alabama. He pursued classical studies at Lagrange, Virginia and at Emory and Henry College, Emory, Virginia, and studied law at the University of Virginia. He was admitted to the Alabama bar and practiced law at Huntsville, Alabama. During the Civil War, he served as a lieutenant colonel on the staff of General James Longstreet in the Confederate Army.
Garth was elected in 1876 as a Democratic representative to the 45th Congress, but was defeated for reelection in 1878. He resumed the practice of law, and died in Huntsville, Alabama on February 25, 1912. He was buried in Maple Hill Cemetery in Huntsville.