Alder is an unincorporated community and census-designated place (CDP) in Madison County, Montana, United States.

According to the U.S. Census Bureau, the Alder CDP has a total area of 2.01 square miles (5.2 km2), all land.

33.3% of all households were made up of individuals, and 16.7% had someone living alone who was 65 years of age or older.

There were no families and 1.8% of the population living below the poverty line, including no under eighteens and none of those over 64.

The Madisonian is a newspaper serving the Madison and Ruby Valleys, which includes Twin Bridges.

[12] Alder is mentioned in the song "Myrna Loy", by American songwriter Josh Ritter, from his 2017 album Gathering.