John T. Lonsdale (November 8, 1895 - October 5, 1960) was an American geologist and educator. Born in Dale, Iowa, he attended elementary school at Dale and high school at Guthrie Center. From there he entered the University of Iowa, from which he received a Bachelor of Arts degree in 1917 and a Master of Science degree in 1921. He served in the U.S. Army as a first lieutenant during World War I, and briefly considered a career in the Army before returning to Iowa to finish his master's degree. After graduating from the University of Iowa, he was named an Assistant Professor of Geology at the University of Virginia and was also an Assistant Geologist with the Geological Survey of Virginia, positions he held until 1924. He received his Ph.D. in Geology from the University of Virginia in 1924. Later that year he became an Assistant Professor of Geology at the University of Oklahoma and worked as a field geologist for the Oklahoma Geological Survey during the summers of 1924 and 1925. He joined the staff at the Texas Bureau of Economic Geology in 1925 as an associate geologist. He was promoted to geologist in 1927. He was a professor of Geology and the chair of the geology department at Texas A. and M. from 1928 until 1935, when he left to go to the Iowa State College where he held the same positions until 1942. From 1942 until 1945 he returned to Army life as a Lieutenant Colonel and then a Colonel and served on the General Staff Corps. He remained in the U.S. Army Reserve until 1953. He became the Director of the Texas Bureau of Economic Geology in 1945, as well as a Professor of Geology at the University of Texas. He held these positions until he unexpectedly died of a heart attack. He married Edna Gertrude von Arnam on August 13, 1921. Lonsdale's ashes were interred at Arlington National Cemetery.