According to the 2009 census, the region has a population of 591,886 which constitutes 1.29% of the population of Spain, with the population density numbering 106.8 people per kilometre. The average life expectancy for male inhabitants is 75 years; for female inhabitants, it is 83 years. Eight years later in 2017 the population has fallen to 581,477 according to INE.

In relative contrast to other regions of Spain, Cantabria has not experienced much immigration. In 2007, only 4.7% of the population were immigrants. The predominant countries of origin for immigrants to Cantabria are Colombia, Romania, Ecuador, Peru, Moldova, and Morocco.

The majority of the population resides in the coastal area, particularly in two cities: Santander, with 183,000 people, and Torrelavega, the second largest urban and industrial centre in Cantabria, having a population of around 60,000. These two cities form a conurbation known as the Santander-Torrelavega metropolitan area. Castro Urdiales has an official population of 28,542, making it the fourth largest in the region because of its proximity to the Bilbao metropolitan area, there are a large number of people not registered in Castro Urdiales, and the true count may be double the official figure.

The most populated municipalities of Cantabria as of 2018 are the following:

Santander (pop. 172,044)

Torrelavega (pop. 51,687)

Castro-Urdiales (pop. 31,977)

Camargo (pop. 30,263)

Piélagos (pop. 25,223)

El Astillero (pop. 18,108)

Santa Cruz de Bezana (pop. 12,964)

Laredo (pop. 11,148)

Santoña (pop. 11,050)

Los Corrales de Buelna (pop. 10,910)

Reinosa (pop. 9,095)