Also, one of the largest limestone mines in Northern Europe is located in the municipality.

On 1 October 1875 the eastern district (population: 1,162) was separated to become the new Velfjord Municipality.

On 1 January 1923, the large village of Brønnøysund (population: 948) was separated from Brønnøy Municipality to become a town (ladested).

[7] The municipality (originally the parish) is named after the small island of Brønnøya (Old Norse: Brunnøy), since the first Brønnøy Church was built there.

On 6 January 1908, a royal resolution changed the spelling of the name of the municipality to Brønnøy.

The official blazon is "Or a balisage signal sable" (Norwegian: I gull en svart seilingsgrind).

The municipality has great scenic variety with numerous islets, lakes (such as Eidvatnet, Sausvatnet, and Fjellvatnet), mountains, and some fertile agricultural areas.

In the southwest is the island of Torget, with the mountain Torghatten, is famous for a cavity that goes straight through the structure.

Lomsdal–Visten National Park is located in the northeastern part of Brønnøy Municipality.

Brønnøy has a temperate oceanic climate with mild winters with all monthly mean temperatures above freezing (Koppen Cfb).

The municipal council (Kommunestyre) of Brønnøy is made up of 23 representatives that are elected to four year terms.

The tables below show the current and historical composition of the council by political party.