The first meeting for the organization of the Thunder Bay District Municipal League was held in the Kam Club in Fort William on April 27, 1917. The first Convention was held in the City Hall in Fort William on November 15 and 16, 1917. The Members consisted of the City of Thunder Bay, the organized Townships and the Statute Labour Board in the Electoral District of Fort William.

The organization was then known as the Fort William District League.

In the spring Convention in 1936, delegates from the Port Arthur District were present and were invited to join the League. At the Fall Convention of the same year, Port Arthur District formally joined the League. It was then that the name was changed to Thunder Bay District Municipal League. Conventions were then held alternately in Port Arthur and Fort William.

In March of 1947, a meeting was held for the representatives from the Thunder Bay District Municipal League, the Rainy River District Municipal Union and the Kenora District Municipal Association for the purpose of forming a union of the three groups. The purpose of this union was to strengthen the League's position when submitting requests to the Provincial Government in Queen's Park, Toronto.

The resulting union from that meeting created the formation of the External link opens in new tab or windowNorthwestern Ontario Municipal Association (NOMA). NOMA holds a convention annually and has had a great influence on the growth and enhancement of Northwestern Ontario.

Until 1957, the Municipal League continued to meet in the spring and Fall of each year. Some League members attended the annual meeting of NOMA as well. In 1958, the League adopted a revised Constitution that changed the procedure of meetings to four times a year.

There was a major revision to the Constitution in March 1996 and many provisions in the Constitution were adopted into Bylaws and Policies. The League still holds their Annual Meeting and Conference but the quarterly meetings were replaced with two general meetings held in the months of June and November. In 1999, a further amendment was made and the League then held their Annual Meeting & Conference in March and a Fall Meeting in October or November. At that time it was also decided that the Board would meet bi-monthly at a location that would be central to the communities. (Red Rock or Nipigon)

A revision to the Constitution was done in 2015 with the final document to be approved at the AGM in 2016. One of the decisions was to delete the spring meeting and hold only one conference in the fall with an Annual meeting at that time. The fiscal year was changed to end August 31st.

In 1996 the City of Thunder Bay withdrew its membership from the League, however, they were allowed separate status in NOMA and remained a member of that organization. The City rejoined the League in the year 2000 and the League again represented all the communities in the District of Thunder Bay. The Township of White River, the Municipality of Wawa and the Township of Hornepayne became members in the League in 1989, 2007 and 2010 respectively. Wawa withdrew from the League in 2013 but the township of Dubreuilville joined that same year. Dubreuilville withdrew in 2014.

Issues that are local in nature and particularly applicable to the Member Municipalities are discussed at the Municipal League meetings. Issues of a broader nature concerning the three Districts united in NOMA are then handled at their meetings. If Members feel that a higher government should review a specific matter, the item is channeled through NOMA and then onto the Association of Municipalities of Ontario (AMO). From there the voice of Northwestern Ontario is transmitted to the appropriate level of Provincial or Federal Government.