Wartau is a municipality in the Werdenberg constituency of the Swiss canton of St. Gallen. The municipality consists of a number of villages on the eastern flank of the Alvier group, along the left shore of the Alpine Rhine.

Wartau municipality consists of the villages of Azmoos (482 m, 1,581 ft), Trübbach (478 m, 1,568 ft), Weite (469 m, 1,539 ft) along the Rhine, Oberschan (668 m, 2,192 ft), Malans (617 m, 2,024 ft), Gretschins (600 m, 2,000 ft) and Fontnas (542 m, 1,778 ft) in the foothills of the Alvier chain, the hamlets of Plattis (464 m, 1,522 ft) and Murris (470 m, 1,540 ft), and Matug (731 m, 2,398 ft) and environs, historically a Walser Streusiedlung.

Wartau has an area, (as of the 2004/09 survey) of 41.75 km² (16.12 sq mi). Of this area, about 45.8% is used for agricultural purposes, while 38.4% is forested. Of the rest of the land, 6.8% is settled (buildings or roads) and 9.0% is unproductive land. In the 2004/09 survey a total of 171 ha (420 acres) or about 4.1% of the total area was covered with buildings, an increase of 46 ha (110 acres) over the 1984 amount. About 0.19% of the total area is recreational space. Of the agricultural land, 26 ha (64 acres) is used for orchards and vineyards, 892 ha (2,200 acres) is fields and grasslands and 1,232 ha (3,040 acres) consists of alpine grazing areas. Since 1984 the amount of agricultural land has decreased by 85 ha (210 acres). Over the same time period the amount of forested land has increased by 56 ha (140 acres). Rivers and lakes cover 104 ha (260 acres) in the municipality.

The highest point of the municipality is Alvier peak, at 2,343 m (7,687 ft), the lowest point is the Rhine Valley at 461 m (1,512 ft).

Wartau has a population (as of December 2020^[update]) of 5,296. As of 2015^[update], 28.6% of the population are resident foreign nationals. In 2015 a small minority (321 or 6.1% of the population) was born in Germany a small minority (273 or 5.2% of the population) was born in Italy. Over the last 5 years (2010-2015) the population has changed at a rate of 3.73%. The birth rate in the municipality, in 2015, was 10.5, while the death rate was 8.6 per thousand residents.

As of 2015^[update], children and teenagers (0–19 years old) make up 22.5% of the population, while adults (20–64 years old) are 61.1% of the population and seniors (over 64 years old) make up 16.4%. In 2015 there were 2,179 single residents, 2,443 people who were married or in a civil partnership, 243 widows or widowers and 366 divorced residents.

In 2015 there were 2,176 private households in Wartau with an average household size of 2.38 persons. In 2015 about 67.1% of all buildings in the municipality were single family homes, which is greater than the percentage in the canton (60.5%) and greater than the percentage nationally (57.4%). Of the 1,446 inhabited buildings in the municipality, in 2000, about 69.3% were single family homes and 14.2% were multiple family buildings. Additionally, about 29.6% of the buildings were built before 1919, while 11.0% were built between 1991 and 2000. In 2014 the rate of construction of new housing units per 1000 residents was 7.66. The vacancy rate for the municipality, in 2016^[update], was 0.82%.

As of 2007^[update], about 23.3% of the population was made up of foreign nationals. Of the foreign population, (as of 2000^[update]), 84 are from Germany, 176 are from Italy, 424 are from ex-Yugoslavia, 53 are from Austria, 25 are from Turkey, and 155 are from another country. Most of the population (as of 2000^[update]) speaks German (88.5%), with Albanian being second most common (3.2%) and Italian being third (2.9%). Of the Swiss national languages (as of 2000^[update]), 4,161 speak German, 9 people speak French, 135 people speak Italian, and 11 people speak Romansh.