Pianist Bennett Lerner had permission from Copland to search through the boxes of sketches and manuscripts in the composer's house in Peekskill, NY. Lerner came upon a sketch from 1944. After playing it for Copland, Lerner edited it to become Midday Thoughts. The published piece is dedicated to Lerner who was responsible for the first performance and recording.
"The same or similar music" to In Evening Air had earlier appeared in the 1944 piano work Midday Thoughts, in the documentary film score The Cummington Story, and in the Clarinet Concerto, writes biographer Howard Pollack (Aaron Copland: The Life and Work of an Uncommon Man, p.515). The piece shares its title with a 1964 poem by Theodore Roethke, the last two lines of which are printed at the end of the score (Pollack p.410).