The town lies on the Abens river, a tributary of the Danube, around eight kilometres from the river's source. The area around Abensberg is characterized by the narrow valley of the Danube, where the Weltenburg Abbey stands, the valley of the Altmühl in the north, a left tributary of the Danube, and the famous Hallertau hops-planting region in the south. The town is divided into the municipalities of Abensberg, Arnhofen, Holzharland, Hörlbach, Offenstetten, Pullach and Sandharland.

Since the administrative reforms in Bavaria in the 1970s, the town also encompasses the following Ortsteile:

There had been settlement on this part of the Abens river since long before the High Middle Ages, dating back to Neolithic times. Of particular interest and national importance are the Neolithic flint mines at Arnhofen, where, around 7,000 years ago, Stone Age people made flint, which was fashioned into drills, blades and arrowheads, and was regarded as the steel of the Stone Age. Traces of over 20,000 individuals were found on this site. The modern history of Abensberg, which is often incorrectly compared with that of the third century Roman castra (military outpost) of Abusina, begins with Gebhard, who was the first to mention Abensberg as a town, in the middle of the twelfth century. The earliest written reference to the town, under the name of Habensperch, came from this time, in around 1138. Gebhard was from the Babonen clan.

In 1256, the castrum of Abensprech was first mentioned, and on 12 June 1348, Ludwig, Margrave of Brandenburg, and his brother, Stephen, Duke of Bavaria, raised Abensberg to the status of a city, giving it the right to operate lower courts, enclose itself with a wall and hold markets. The wall was built by Ulrich III, Count of Abensberg. Some of the thirty-two round towers and eight turrets are still preserved to this day.

In the Middle Ages, the people of Abensberg enjoyed a level of autonomy above their lord. They elected a city council, although only a small number of rich families were eligible for election.

In around 1390, the Carmelite Monastery of Our Lady of Abensberg was founded by Count John II and his wife, Agnes. Although Abensberg was an autonomous city, it remained dependent on the powerful Dukes of Bavaria. The last Lord of Abensberg, Nicholas, supposedly named after his godfather, Nicholas of Kues, a Catholic cardinal, was murdered in 1485 by Christopher, a Duke of Bavaria-Munich. The year before, Nicholas had unchivalrously taken Christopher captive as he bathed before a tournament in Munich. Although Christopher renounced his claim for revenge, he lay in wait for Nicholas in Friesling. When the latter arrived, he was killed by Seitz von Frauenberg. He is buried in the former convent of Abensberg. Abensberg then lost its independence and became a part of the Duchy of Bavaria, and from then on was administered by a ducal official, the so-called caretaker. The castle of Abensberg wasdestroyed during the Thirty Years' War, although the city had bought a guarantee of protection from the Swesidh general, Carl Gustaf Wrangel. Johannes Aventinus (1477–1534) is the city's most famous son, the founder of the study of history in Bavaria. Aventinus, whose name was real name is Johann or Johannes Turmair (Aventinus being the Latin name of his birthplace) wrote the Annals of Bavaria, a valuable record of the early history of Germany and the first major written work on the subject. He is commemorated in the Walhalla temple, a monument near Regensburg to the distinguished figures of German history. Until 1800, Abensberg was amunicipality belonging to the Straubing district of the Electorate of Bavaria. Abensberg also contained a magistrates' court. In the Battle of Abensberg on 19–20 April 1809, Napoleon gained a significant victory over the Austrians under Archduke Louis of Austria and General Johann von Hiller.

The arms of the city are divided into two halves. On the left are the blue and white rhombuses of Bavaria, while the right half is split into two sliver and black triangles. Two diagonally-crossed silver swords with golden handles rest on top.

The town has had a coat of arms since 1338, that of the Counts of Abensberg. With the death of the last Count, Nicholas of Abensberg, in 1485, the estates fell to the Duchy of Bavaria-Munich, meaning that henceforth only the Bavarian coat of arms was ever used.

On 31 December 1809, a decree of King Maximilian of Bavaria granted the city a new coat of arms, as a recognition of their (mainly humanitarian and logistic) services in the Battle of Abensberg the same year. The diagonally divided field in silver and black came from the old crest of the Counts of Abensberg, while the white and blue diamonds came from that of the House of Wittelsbach, the rulers of Bavaria. The swords recall the Battle of Abensberg.

The district of Offenstetten previously possessed its own coat of arms.