District 9 formed and began meeting before it received its charter in 1902. In its early years, membership fluctuated annually 1155 members in 1901, 742 in 1902, 1047 in 1903, and 950 in 1907) with “lack of interest” and “unemployment” accounting for the declines. Since the trade was well-defined, District 9 estimated that 90-98% of machinists were organized from 1900-1910. In 1907 the international held its convention in St. Louis. District 9 developed into a strong, well-administered, and highly independent union. Several strikes occurred annually, with the greatest number coming during World War I. Between 1916-1920, the district dismissed over 200 members for being scabs. F.M. Parmeter who was the Secretary-Treasurer from 1912 to 1927, and assistant business agent until 1934, conducted the district’s business and guided it into its position as one of the strongest in the union. In 1921 and 1938 District 9 won appeals against the national policy on dues.
In 1939 District 9 had 16 affiliated locals, Local 41-St. Louis, MO; Local 121-E. St. Louis, MO; Local 313-E. St. Louis, MO; Local 353-Belleville, IL; Local 394-St. Louis, MO; Local 407-Belleville, IL; Local 572-Granite City, IL; Local 660-Alton, IL; Local 688-St. Louis, MO; Local 710-St. Louis, MO; Local 738- St. Louis, MO; Local 777-St. Louis, MO; Local 787-St. Louis, MO; Local 1107-Granite City, IL; Local 1262-Alton, IL, and Local 1345-St. Louis, MO. On January 1, 1965 the name was changed once again to the International Association of Machinists and Aerospace Workers. Currently District 9 has 10 affiliated locals, Local 41-St. Louis, MO; Local 313 -Caseyville, IL; Local 660-E. Alton, IL; Local 688-St. Louis, MO; Local 777-St. Louis, MO; Local Lodge 822 – Quincy, IL; Local 1345-St. Louis, MO; Local 1745-Warrenton, MO, Local 1815-Springfield, IL and Local 2782-West Plains, MO.