King wrote the first draft of IT between August 1980 and June 1981. Before putting the first sheet into his typewriter he had been developing his ideas for IT for about five years, as he told The Bangor Daily News in July 1980.^​1​ King did not take notes or write outlines or character studies beforehand; all that work went on in his head.

Another project, begun in 1978, heavily stimulated his preparatory thinking about IT, so much so that the two texts can be seen as two sides of the same coin. The project became King’s first novel-length work of nonfiction, Danse Macabre, published in April 1981 by Everest House. He wrote the first draft in 1979, did an extensive rewrite of the text in the spring of 1980 in preparation of submission, and turned his attention to IT immediately afterwards.