The castle in the town center was built in 950 on a hill, the first houses of Monthey surrounded it.

During the first part of the 14th century, there were several industries including silk production and grinding mills.

Monthey has an area, as of 2009[update], of 28.6 square kilometers (11.0 sq mi).

This urban center of the Chablais region is located on an alluvial fan of the Vieze on the left bank of the Rhône, at the entrance to Val d'Illiez and the Pas de Morgins which leads to Val d'Abondance.

It consists of the town of Monthey, the villages of Outrevièze and Choëx and exclaves in Collombey-Muraz.

Monthey is located on the west side of the Rhône valley, south to the Leman Lake.

The blazon of the municipal coat of arms is Or, issuant from coupeaux Vert an Oak tree proper leaved and fructed of the second.

[8] Most of the population (as of 2000[update]) 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%).

[8] In winter 2005, Monthey was chosen to be the host of the EYOF (European Youth Olympic Festival).

[14] In the 2007 Swiss Council of States election a total of 4,131 votes were cast, of which 413 or about 10.0% were invalid.

[15] Monthey is important to Swiss industry, with the former chemical company Ciba-Geigy (now Novartis, Syngenta and Cimo) and the metallurgical company Giovanola, there is an oil refinery in Collombey-Muraz, near Monthey.

The city is close to the famous winter sports region, the Portes du Soleil.

This city is also home to Bolliger & Mabillard, world-famous roller coaster designers.

The number of jobs in the primary sector was 19, of which 15 were in agriculture and 3 were in forestry or lumber production.

In the tertiary sector; 1,087 or 25.0% were in wholesale or retail sales or the repair of motor vehicles, 125 or 2.9% were in the movement and storage of goods, 287 or 6.6% were in a hotel or restaurant, 69 or 1.6% were in the information industry, 156 or 3.6% were the insurance or financial industry, 405 or 9.3% were technical professionals or scientists, 203 or 4.7% were in education and 1,504 or 34.7% were in health care.

[8] From the 2000 census[update], 9,790 or 70.3% were Roman Catholic, while 1,381 or 9.9% belonged to the Swiss Reformed Church.