Simeon Timothy "Sim" Lake III (July 4, 1944, Chicago, Illinois) is an American judge and attorney who has served on the United States District Court for the Southern District of Texas since 1988. He notably presided over the the trial of Enron Chairman Ken Lay and former Chief Executive Officer Jeff Skilling.

Lake graduated from Texas A&M University in 1966 and was number one in his class at the University of Texas School of Law in 1969 . He served in U.S. Army from 1970 to 1971 as a Judge Advocate General's Corps prosecutor in Vietnam, then worked at the law firm of Fulbright & Jaworski LLP in Houston, Texas through most of 1972 to the late 1980s. He was appointed as a judge on the U.S. District Court's Southern District of Texas in 1988 by President Ronald Reagan.

Prior to Enron, in other notable cases: