The story of corn flakes goes back to the late 19th century, when a team of Seventh-day Adventists began to develop new foods to adhere to the vegetarian diet recommended by the church. Members of the group experimented with a number of different grains, including wheat, oats, rice, barley and maize. In 1894, John Harvey Kellogg, the superintendent of the Battle Creek Sanitarium in Michigan and an Adventist, used these recipes as part of a strict vegetarian regimen for his patients, which also included no alcohol, tobacco or caffeine. The diet he imposed consisted entirely of bland foods. A follower of Sylvester Graham, the inventor of graham crackers and graham bread, Kellogg believed that spicy or sweet foods would increase passions.

This idea for corn flakes began by accident when Kellogg and his younger brother, Will Keith Kellogg, left some cooked wheat to sit while they attended to some pressing matters at the sanitarium. When they returned, they found that the wheat had gone stale, but being on a strict budget, they decided to continue to process it by forcing it through rollers, hoping to obtain long sheets of the dough. To their surprise, what they found instead were flakes, which they toasted and served to their patients. This event occurred on August 8, 1894, and a patent for "Flaked Cereals and Process of Preparing Same" was filed on May 31, 1895, and issued on April 14, 1896.

A newspaper advertisement for Kellogg's Toasted Corn Flakes in 1919.
Dr Kellogg introduced Kellogg's Corn Flakes in hopes that it would reduce dyspepsia and, in accordance with the practices of the Seventh-day Adventists, masturbation and excessive sexual intercourse.

The flakes of grain, which the Kellogg brothers called granose, were a very popular food among the patients. The brothers then experimented with other flakes from other grains. In 1906, Will Keith Kellogg, who served as the business manager of the sanitarium, decided to try to mass-market the new food. At his new company, Battle Creek Toasted Corn Flake Company, he added sugar to the flakes to make them more palatable to a mass audience, but this caused a rift between his brother and him. In 1907, his same company ran an ad campaign which offered a free box of cereal to any woman who winked at her grocer. To increase sales, in 1909 he added a special offer, the Funny Jungleland Moving Pictures Booklet, which was made available to anyone who bought two boxes of the cereal. This same premium was offered for 22 years. At the same time, Kellogg also began experimenting with new grain cereals to expand his product line. Rice Krispies, his next great hit, first went on sale in 1928.

There have been many mascots of Kellogg's Cornflakes. The most popular one is a green rooster named Cornelius "Corny" Rooster, which has been the mascot since his debut. In early commercials, he would speak the catch phrase "Wake up, up, up to Kellogg's Cornflakes!" Dallas McKennon and Andy Devine voiced him. Later, he stopped talking and simply crowed. The concept of using a stylized cockerel originated from a suggestion by family friend Nansi Richards, a harpist from Wales and a Welsh language proponent. The Welsh word for cockerel is ceiliog (pronounced keyeleeog or in some dialects keelog).