The name Achstetten is derived from the Old High German words aha meaning water, and stet, meaning place; the name meaning thus place close to water.
The Hil(de)gartstraße in Achstetten is a reminder of an early mediaeval trade route. It is a relic of a route leading from Konstanz via Meersburg towards Ulm and then further via Heidenheim to Aalen and Würzburg, terminating at Fulda. There is evidence to indicate that a road towards the crossing of the river Iller branched off on the territory of Achstetten. This road would then lead on towards Regensburg.
Achstetten was first mentioned in a charter dated 1194. This charter was signed by Pope Celestine III, confirming the rights of Wiblingen Abbey in Asteten. The possessions of the monastery of Wiblingen in Achstetten were, however, certainly older than 1194.
From 1356 to 1447, the Freiherrn von Freyberg were the sole rulers of Achstetten. In 1442, the rule over Achstetten was divided amongst three brothers, Eberhard von Freyberg, Hans von Freyberg and Wilhelm von Freyberg. However, in 1447, Wilhelm von Freyberg sold his part to Gutenzell Abbey. As a consequence, the Freiherrn von Freyberg were forced to share the rule of the village with Gutenzell Abbey until 1625.
Through marriage, the two remaining parts of Achstetten came into the possession of the Counts of Öttingen-Spielberg in 1689. They exchanged it in 1765, so that from 1765 on, it was part of the landed territories of the Freiherrn von Welden. The Freiherrn von Welden sold it on 12 May 1795 to the last Komtur of the Teutonic Knights, the Freiherr Beat Conrad Reuttner von Weyl. He transferred his possession to his nephew Julius Cäsar Reuttner von Weyl, who, in 1802, bought the rights of the revenue from the complete tithes from Ochsenhausen Abbey. He was elevated to the rank of count in 1819. To this day, his successors are owners of the Lordship of Achstetten.
After having initially been part of the district of Wiblingen, it became part of the district of Laupheim in 1845. On 1 October 1938, Achstetten became part of the district of Biberach.
On 1 March 1972, the formerly independent municipality of Oberholzheim was incorporated into Achstetten, followed on 1 November 1972 by Bronnen and on 1 January 1975 by Stetten.
Originally, Achstetten was part of the parish of Laupheim. It became an independent parish in 1442, when the Freiherrn von Freyberg founded a new parish, subordinate to the monastery of Ochsenhausen.
The gallery is separated into two parts, one part designated for the general public, and a second part into which only the former rulers of Achstetten, members of the dynasty of Reuttner von Weyl, were permitted. The compartment for the aristocracy is connected to the castle by a passageway, built on wooden columns. A similar structure existed in Laupheim. There, however, the passageway is only preserved in fragments.
A re-building of the castle at the same location was mentioned in 1583, while, around 1620, the abbot of the monastery of Ochsenhausen referred to the newly erected castle as being a magnificent building.
The last Komtur of the Teutonic Knights, the Freiherr Beat Conrad Reuttner von Weyl, had the castle renovated by the official architect of the Teutonic Knights, Franz Anton Bagnato, between 1794 and 1796. Franz Anton Bagnato's design consists of a simple, un-adorned three-storey builing, containing the living quarters, as well as two economy wings. The interior contains nowadays antique furniture, a stove from 1798, and family portraits of members of the family of Reuttner von Weyl.
The original castle park is home to an enclosure where fallow deer are kept.