Delmenhorst (German pronunciation: [ˈdɛlmənˌhɔʁst] ⓘ; Northern Low Saxon: Demost) is an urban district (Kreisfreie Stadt) in Lower Saxony, Germany.

Delmenhorst was first mentioned in a charter in 1254, after the Count of Oldenburg, Otto I, bought the place near the river Delme in 1234.

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.

In the 1930s Great Depression the Nordwolle went bankrupt - nevertheless the town grew bigger, incorporating several smaller villages around it.

After the Second World War, Delmenhorst was in the British zone of occupation and had to deal with thousands of refugees from Eastern Germany, which now was occupied by the Soviet Union.

Since the 1960s there has been a steady decrease in employment, leaving more than 13% of the town's inhabitants unemployed and nearly 7% living on social welfare.

The Hanse-Wissenschaftskolleg (HWK) Institute for Advanced Study is located at Delmenhorst, in the neighborhood of Deichhorst.