When did ragtime music come popular?

Originally Ragtime was popular in St. Louis and New Orleans when it originated during the early part of the 20th century (1900's). Later it was revived, first in the 40's, then again in the 50's, and finally in the 70's when lots of new recordings of old Ragtime standards came out. For example, the movie The Sting featured Scott Joplin's The Entertainer which went on to become #3 on the Billboard top 100. This in turn led to a Ragtime revival (yet again) but by then it was widespread.