Delmenhorst (German pronunciation: [ˈdɛlmənhɔʁst]) is an urban district (Kreisfreie Stadt) in Lower Saxony, Germany. It has a population of 74,500 and is located 10 km/6 miles west of downtown Bremen with which it forms a contiguous urban area, whereas the city of Oldenburg is 25 km/15 miles to the northwest. The city has a total area of 62.36 km² and a population density of approx. 1200 inhabitants per km².

Since 2006 it is governed by the mayor Patrick de la Lanne.

Delmenhorst was first mentioned in a charter in the year 1254, after the Count of Oldenburg, Otto I, bought the place near the river Delme in 1234. A castle to protect the newly founded settlement was established in about 1247. The following count, Otto II, made the castle his residency; Delmenhorst was declared an independent town on 15 July 1371 under Bremen's law.

After a short period under the governance of the bishop of Bremen from 1421 to 1436 Delmenhorst returned under the custody of Oldenburg. Delmenhorst later was infamous for its robber-baronship under the count Gerd. Its reign ended in 1482 thanks to a siege laid to the castle under the leadership of the bishop of Münster. Therefore the town now was under Münster authority until finally count Anton I won back the town as well as the castle in 1547.