Altnau is a municipality in the district of Kreuzlingen in the canton of Thurgau in Switzerland.

The vogt right over the church's farms belonged to the Freiherr of Altenklingen after 1300.

In 1454 the villagers were represented in the Appenzell Landrecht, but following complaints from Constance they were forced to give up their membership.

About 1880 a dairy company was founded in the village, and livestock and cheese production became common.

In 1840 the Seestrasse (Lake Road) was built, and in 1870, the Seetalbahn (railroad line) was added.

[3] Altnau has an area, as of 2009[update], of 6.68 square kilometers (2.58 sq mi).

Of the rest of the land, 0.93 km2 (0.36 sq mi) or 13.9% is settled (buildings or roads), 0.02 km2 (4.9 acres) or 0.3% is either rivers or lakes.

[4] The municipality is located in the Kreuzlingen district along the Romanshorn-Kreuzlingen road about 2 km (1.2 mi) from Lake Constance.

[6] The age distribution, as of 2009[update], in Altnau is; 199 children or 10.0% of the population are between 0 and 9 years old and 295 teenagers or 14.9% are between 10 and 19.

[12] In the 2007 federal election the most popular party was the SVP which received 38.69% of the vote.

[13] The historical population is given in the following table:[3][14] The entire village of Altnau is designated as part of the Inventory of Swiss Heritage Sites.

[7] From the 2000 census[update], 570 or 31.6% were Roman Catholic, while 881 or 48.8% belonged to the Swiss Reformed Church.

Of the children in kindergarten, 18 or 40.9% were female, 7 or 15.9% were not Swiss citizens and 2 or 4.5% did not speak German natively.

The lower and upper primary levels begin at about age 5-6 and last for 6 years.

At the lower primary level, there were 26 children or 44.1% of the total population who were female, 5 or 8.5% were not Swiss citizens and 1 or 1.7% did not speak German natively.

In the upper primary level, there were 35 or 47.9% who were female, 6 or 8.2% were not Swiss citizens and 3 or 4.1% did not speak German natively.

There were 178 teenagers who were in the advanced school, of which 97 or 54.5% were female, 15 or 8.4% were not Swiss citizens and 7 or 3.9% did not speak German natively.

There were 95 teenagers who were in the standard school, of which 47 or 49.5% were female, 23 or 24.2% were not Swiss citizens and 18 or 18.9% did not speak German natively.