Who do you call to report polygamy?

Answer 1

If polygamy is illegal in the area of where you reside, then normal you would call your local authority. Again, depending on the location, normally the police would not arrest those practicing polygamy right away (referring to the United States). Normally the police would report the act to a high power like the State Department.

Answer 2

You could contact local authorities (police) to report polygamy. Depending on the local laws and policies, they may not be able to do anything. Most polygamists do not seek official marriages with their spouses - they may live together as husband and wives, but are not technically 'married' by the laws of the land and therefore may not be doing anything illegal, unless cohabitation or adultry laws in your area apply.