If you are referring to what Christians call "satanism", which is really devil worship:\n\n"This form of Satanism was invented by the Roman Catholic Church in the 15th century CE, just prior to the time of the Witch burnings."  (first source)\n\n\nIf you mean satanism as a religion apart from Christianity:\n\n"Religious Satanists existed in the 1950's, both in the United States and the UK. But they were little known to the public." (second source)