Thetus Willrette Sims was an American politician and a member of the United States House of Representatives for the 8th congressional district of Tennessee. He was born on April 25, 1852 near Waynesboro, Tennessee in Wayne County. He attended a private school at Martin Mills and moved with his parents to Savannah, Tennessee in Hardin County in 1862. He attended Savannah (Tennessee) College and graduated from Cumberland School of Law at Cumberland University in Lebanon, Tennessee in June 1876. He was admitted to the bar the same year. He commenced practice in Linden, Tennessee in Perry County. He was the superintendent of public instruction for Perry County, Tennessee from 1882 to 1884.
Thetus Sims was elected to the House in the fall of 1896 as a Democrat. He was reelected to the eleven succeeding Congresses.
His tenure in the House lasted for 12 terms in office from March 4, 1897 to March 3, 1921.
He returned to Tennessee and resumed the practice of law in Lexington, Tennessee in Henderson County for a few years. He retired from active business pursuits in 1930 shortly after the beginning of the Great Depression and returned to Washington, D.C., where he died on December 17, 1939 (aged 87). He was interred in Rock Creek Cemetery in Washington, D.C.