Ilya Andreyevich Tolstoy (3 February 1903 – 28 October 1970), count, U.S. Army Colonel. President F. D. Roosevelt's envoy in Tibet. He was one of the founders of Marineland of Florida, of the Bahamas National Trust, and he served on the Caribbean Conservation Commission. He was a grandson of count Lev Tolstoy.
Count Ilya Tolstoy was born in 1903 at Toptivovo, Tula, Russia. His father was Count Andrey Lvovich Tolstoy, son of writer Lev Tolstoy, and his mother was Olga Diterichs, daughter of General of the Infantry Konstantin Diterichs (and sister of General Mikhail Diterikhs). Tolstoy attended the Moscow School of Agriculture, before joining the Imperial Cavalry and serving in Tashkent. In 1917 – 1918 he worked for the Russian Department of Agriculture in Turkestan.
Tolstoy emigrated to the United States in 1924. He studied at the William Penn College and Iowa State University, Ames.
In 1927, Tolstoy became associated with the explorer and naturalist, William Douglas Burden, an associate and trustee of the American Museum of Natural History. He was inducted into the Explorers Club in New York in 1931.  Tolstoy was one of the pioneers of underwater photography and one of the founders and owners of the world's first oceanarium, Marineland of Florida with William Douglas Burden, Cornelius Vanderbilt Whitney and Sherman Pratt.
In World War II Tolstoy was an officer in the Office of Strategic Services. He went to Tibet as an envoy of the US President Franklin D. Roosevelt in 1942 and met the Dalai Lama, then barely seven years old. In 1945 he headed a top-secret mission into the interior of China of search of uranium.
His first marriage in 1920 was to Zoya Dmitrievna Platonova (born on 18 December, 1891, died on 27 September, 1978). His son Count Alexander Tolstoy was born in 1921. His second marriage was to Vera Ilinichna Sidorkova (born on 28 September, 1894, died on 10 August, 1974), by whom he had a daughter, Sofija, born in 1922. The marriage ended in divorce.
Tolstoy died on 28 October, 1970 in New York and was buried in the cemetery of the Novo-Diveevo Cemetery, Nanuet, New York, USA.