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. AMO Bylaw No. 2 was adopted in August, 2012. In August 2019, it was amended to address several circumstances arising from the previous municipal election.