Altenstadt is a municipality in the district Wetteraukreis, in Hesse, Germany. It is situated in the Nidder valley, approx. 27 kilometers north-east of Frankfurt am Main.

Altenstadt was part of the limes, the former border of the Roman Empire, that passes through the town. According to excavations, Altenstadt was a Roman garrison in the first half of the second century.

The first documented mention of Altenstadt took place only in the year 767, which makes Altenstadt the oldest municipality of Upper Hesse.

The municipality consists of 8 districts:

Altenstadt Heegheim Höchst an der Nidder Lindheim

Enzheim Oberau Rodenbach Waldsiedlung

Rudolf Ehrmann was born in Altenstadt in 1879. He became Professor at the Friedrich-Wilhelms-Universität Berlin for Inner Medicine and one of the most prominent German Physician of first half of the 20th century. He was a personal general practitioner to Albert Einstein who helped him to emigrate to the USA in 1939. In 1945 he became a US citizen.

One of the inhabitants of Altenstadt was the justice inspector Friedrich Kellner, who alternated his work-week between Laubach and Altenstadt during World War II. Kellner recorded the misdeeds of the Nazis in a ten-volume diary which was on display in 2005 at the George Bush Presidential Library. A Canadian documentary, My Opposition: the Diaries of Friedrich Kellner, was produced in 2006.

The Lutheran missionary Georg Heinrich Schwarz was born in Höchst an der Nidder in 1868. He laboured in the Cape Bedford Mission, North Queensland, Australia, for 55 years. The anniversary of his arrival is still celebrated there each year in September and known as Muni Day.

On 5 September 2019, Stefan Jagsch from the extreme-right NPD was elected the Mayor of the Waldsiedlung unopposed, which led to irritation in other parties at national level.

• Official site (in German)
• Website of Lindheim (in German)
• Website of Enzheim (in German)
• Der Weltkrieg war vor deiner Tür Altenstadt and the former Airfield Altenstadt in World War II (in German)