Monthey has a population (as of December 2018) of 17,785.
 As of 2008, 29.0% of the population are resident foreign nationals.
Over the last 10 years (2000–2010 ) the population has changed at a rate of 17.5%.
 It has changed at a rate of 16.2% due to migration and at a rate of 3.4% due to births and deaths.

Most of the population (as of 2000) speaks French (11,856 or 85.1%) as their first language, Italian is the second most common (520 or 3.7%) and Portuguese is the third (430 or 3.1%).
 There are 295 people who speak German and 7 people who speak Romansh.

As of 2008, the population was 49.0% male and 51.0% female.
 The population was made up of 5,515 Swiss men (33.6% of the population) and 2,539 (15.4%) non-Swiss men.
 There were 6,171 Swiss women (37.5%) and 2,212 (13.5%) non-Swiss women.
Of the population in the municipality, 4,611 or about 33.1% were born in Monthey and lived there in 2000.
 There were 2,769 or 19.9% who were born in the same canton, while 2,508 or 18.0% were born somewhere else in Switzerland, and 3,586 or 25.7% were born outside of Switzerland.

As of 2000, children and teenagers (0–19 years old) make up 24.1% of the population, while adults (20–64 years old) make up 62.3% and seniors (over 64 years old) make up 13.6%.

As of 2000, there were 5,724 people who were single and never married in the municipality.
 There were 6,463 married individuals, 836 widows or widowers and 910 individuals who are divorced.

As of 2000, there were 5,949 private households in the municipality, and an average of 2.3 persons per household.
There were 2,161 households that consist of only one person and 340 households with five or more people.
 In 2000, a total of 5,697 apartments (80.3% of the total) were permanently occupied, while 1,058 apartments (14.9%) were seasonally occupied and 339 apartments (4.8%) were empty.
 As of 2009, the construction rate of new housing units was 3.6 new units per 1000 residents.
The vacancy rate for the municipality, in 2010, was 0.24%.
Monthey has a population (as of December 2018) of 17,785.  As of 2008, 29.0% of the population are resident foreign nationals. Over the last 10 years (2000–2010 ) the population has changed at a rate of 17.5%.  It has changed at a rate of 16.2% due to migration and at a rate of 3.4% due to births and deaths.
Most of the population (as of 2000) speaks French (11,856 or 85.1%) as their first language, Italian is the second most common (520 or 3.7%) and Portuguese is the third (430 or 3.1%).  There are 295 people who speak German and 7 people who speak Romansh.
As of 2008, the population was 49.0% male and 51.0% female.  The population was made up of 5,515 Swiss men (33.6% of the population) and 2,539 (15.4%) non-Swiss men.  There were 6,171 Swiss women (37.5%) and 2,212 (13.5%) non-Swiss women. Of the population in the municipality, 4,611 or about 33.1% were born in Monthey and lived there in 2000.  There were 2,769 or 19.9% who were born in the same canton, while 2,508 or 18.0% were born somewhere else in Switzerland, and 3,586 or 25.7% were born outside of Switzerland.
As of 2000, children and teenagers (0–19 years old) make up 24.1% of the population, while adults (20–64 years old) make up 62.3% and seniors (over 64 years old) make up 13.6%.
As of 2000, there were 5,724 people who were single and never married in the municipality.  There were 6,463 married individuals, 836 widows or widowers and 910 individuals who are divorced.
As of 2000, there were 5,949 private households in the municipality, and an average of 2.3 persons per household. There were 2,161 households that consist of only one person and 340 households with five or more people.  In 2000, a total of 5,697 apartments (80.3% of the total) were permanently occupied, while 1,058 apartments (14.9%) were seasonally occupied and 339 apartments (4.8%) were empty.  As of 2009, the construction rate of new housing units was 3.6 new units per 1000 residents. The vacancy rate for the municipality, in 2010, was 0.24%.
Monthey