Westerlo is a town in Albany County, New York, United States.

The town is on the southern border of Albany County and is served by New York State Route 143.

Westerlo was formed from parts of the Towns of Coeymans and Rensselaerville in 1815.

As of the census[7] of 2000, there were 3,466 people, 1,326 households, and 970 families residing in the town.

22.2% of all households were made up of individuals, and 9.4% had someone living alone who was 65 years of age or older.