The Casey franchise was started in 1934 by George Harmon Coxe in Black Mask (magazine). A total of 22 stories were published in the magazine, plus two serialized novels. Note the company these stories keep within the pages of Black Mask such as Raymond Chandler & E. Stanley Gardner. This magazine was an important part of the pulp magazine genre.
In addition to these stories, the two earliest novels were serialized over three issues each.