[4] Its composition changed throughout the years, especially in 1998, when the nearby city of Trofa created its own municipality, taking some of Santo Tirso's towns with it.

One of the first textile factories in the region, the Fábrica de Fiação e Tecidos do Rio Vizela, opened in Vila das Aves, part of its municipality, in 1845.

This factory would become the largest of its kind in Portugal, with an area of about nine square kilometres and employing, at one point, over 3.000 people.

Santo Tirso has a Mediterranean climate with warm to hot summers and mild, very wet winters.

Administratively, the municipality is divided into 14 civil parishes (freguesias):[8] Santo Tirso is home of the historic[further explanation needed] football club Futebol Clube Tirsense and C.D.