In June 1980, an Association Review Committee presented its report with recommendations proposing a new association of municipal representatives, "restructured to ensure accurate representation of the positions of the different types of municipalities in the province".

The newly constituted Association of Municipalities of Ontario came into being on January 1, 1982. In May of 1990 AMO became formally incorporated without share capital. AMO's constitution was reformulated into governing By-law No.1.

The By-law has been amended a number of times to implement significant changes to the Association. This By-law was reviewed in 2012 to clarify provisions and reflect new not-for-profit legislation. By-law No. 2 was adopted and By-law No. 1 was repealed.