The Northwestern Ontario Municipal Association is comprised of:
- the Kenora District Municipal Association;
- the Rainy River District Municipal Association,
- the Thunder Bay District Municipal League; and,
- the City of Thunder Bay.
Other than the City of Thunder Bay, membership is attained by being a member of the district organization. The Township of White River in the District of Algoma being a member of the Thunder Bay District Municipal League also has membership into NOMA.
In addition, Associate Memberships are available for purchase by business and not-for-profit corporations.