who said ignorance is bliss

The phrase "ignorance is bliss" was originally coined by the English poet Thomas Gray in his 1742 poem "Ode on a Distant Prospect of Eton College." The full line is "where ignorance is bliss, 'tis folly to be wise," meaning it can be more comfortable not to know certain things than to know them. This phrase has been widely used and referenced since then, including by Thomas Jefferson, who commented on it philosophically.