Masein (Romansh: Masagn) is a municipality in the Viamala Region in the Swiss canton of Graubünden.

Masein is first mentioned in 1156 as de Medezenu.

Masein has an area, as of 2006, of 4.2 km (1.6 sq mi). Of this area, 38.4% is used for agricultural purposes, while 52% is forested. Of the rest of the land, 6% is settled (buildings or roads) and the remainder (3.6%) is non-productive (rivers, glaciers or mountains).

Before 2017, the municipality was located in the Thusis sub-district, of the Hinterrhein district, after 2017 it was part of the Viamala Region. It is located on the lower Heinzenberg and consists of the two settlements of Ober- and Unter-Masein and the hamlets of Dalaus, Cresta und Lochmüli.

Masein has a population (as of 31 December 2020) of 500. As of 2008, 2.8% of the population was made up of foreign nationals. Over the last 10 years the population has grown at a rate of 2.9%.

As of 2000, the gender distribution of the population was 51.0% male and 49.0% female. The age distribution, as of 2000, in Masein is; 46 people or 12.6% of the population are between 0 and 9 years old. 29 people or 7.9% are 10 to 14, and 37 people or 10.1% are 15 to 19. Of the adult population, 38 people or 10.4% of the population are between 20 and 29 years old. 60 people or 16.4% are 30 to 39, 70 people or 19.1% are 40 to 49, and 47 people or 12.8% are 50 to 59. The senior population distribution is 21 people or 5.7% of the population are between 60 and 69 years old, 12 people or 3.3% are 70 to 79, there are 5 people or 1.4% who are 80 to 89, and there is 1 person who is 90 to 99.

In the 2007 federal election the most popular party was the SVP which received 37.7% of the vote. The next three most popular parties were the SPS (33.6%), the FDP (14.8%) and the CVP (11.4%).

The entire Swiss population is generally well educated. In Masein about 80.4% of the population (between age 25-64) have completed either non-mandatory upper secondary education or additional higher education (either university or a Fachhochschule).

Masein has an unemployment rate of 1.21%. As of 2005, there were 32 people employed in the primary economic sector and about 11 businesses involved in this sector. 3 people are employed in the secondary sector and there are 2 businesses in this sector. 47 people are employed in the tertiary sector, with 11 businesses in this sector.

The historical population is given in the following table:

year	population
1803	198
1850	282
1900	228
1950	270
2000	366
2010	409

Most of the population (as of 2000) speaks German (92.6%), with Romansh being second most common ( 3.3%) and Dutch being third ( 1.4%).

Languages in Masein

Languages	Census 1980		Census 1990		Census 2000
	Number	Percent	Number	Percent	Number	Percent
German	188	82.82%	306	91.89%	339	92.62%
Romanish	26	11.45%	15	4.50%	12	3.28%
Italian	6	2.64%	3	0.90%	1	0.27%
Population	227	100%	333	100%	366	100%

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