There are a number of saints named Thomas. You need to be more specific.
Thomas Aquinas was canonized on July 18, 1323, by Pope John XXII.
St. Thomas Aquinas was canonized as a saint in 1323 by Pope John XXII, about 49 years after his death in 1274.
St. Clare of Assisi was canonized on September 26, 1255, by Pope Alexander IV.
St. Etheldreda was canonized by Pope Celestine III in 1198.
St. Thomas Aquinas was officially canonized as a saint on July 18, 1323, by Pope John XXII.
St. Catherine of Siena was canonized by Pope Pius II on June 29, 1461.
Thomas More was canonized in 1935 by Pope Pius XI in the Vatican (Rome).
Maria Goretti was canonized by Pope Pius XII.
It means that Rome has investigated his life thoroughly and the pope is declaring that he is indeed in Heaven.
St. Eligius was canonized in the Pre-Congregation era. This was when people were often canonized because of their popularity while they were alive.
If you are referring to St. Francis of Assisi he was canonized on July 16, 1228, by Pope Gregory IX.
St. Louis IX of France was canonized on August 11, 1297 by Pope Boniface VIII.