The city's name refers to a sand-mud plain located on the left side of the Narew River which regularly flooded in the springtime throughout the centuries.

A small fort was built on an island in the 11th or 12th century, currently located just one kilometer west of the modern city center.

[2] By the beginning of the 15th Century, Ostrołęka grew into an important economic center in the Duchy of Masovia for trade with the neighboring Teutonic Order.

The Golden Age lasted for approximately 40 years, whose conclusion is marked by three major catastrophes which struck in 1564 and 1571.

[citation needed] It was a Polish royal city, administratively located in the Masovian Voivodeship in the Greater Poland Province.

At the turn of the century, the first German and Jewish families began to settle in the town and surrounding areas.

Taking place on the banks of the Narew outside of Ostrołęka where the French, under the General Anne Jean Marie René Savary, prevailed.

[2] As part of a comprehensive plan of industrializing Poland, an extensive settlement for linen and cotton craftsmen was built on the right bank of Narew in 1826.

Although the town's citizens were eager and proud to take part in the November Uprising of 1830-1831, they worried that their city, as in every previous war, would be destroyed.

Rebel plans envisaged the Polish Army attacking the Russian Infantry Corps of the Tsar's Guard, which made camp between Augustów and Ostrołęka.

As a cannonade was heard, Jan Zygmunt Skrzynecki couldn't believe that Hans Karl von Diebitsch (a Russian general) had already reached the suburbs of the city.

[citation needed] Von Diebitsch took over the city center, but the battle continued on the right side of the Narew.

Skrzynecki and his troops valiantly defended the bridge, wanting to hold back the Russian forces from crossing over to the other side of the river.

In 1864, after the Russian government's order, the Benedictines left Ostrołęka and the monastery buildings were placed under the parish-priest authority.

[citation needed] Until the First World War, the city managed to develop, but it was still a relatively unremarkable small town.

To make transporting the wood easier, they built 40 km (25 mi) of road from Ostrołęka to Myszyniec and a narrow-gauge railway line.

On 4 August 1920, Soviet forces under the command of Hayk Bzhishkyan took the fort and "butchered the newly assembled cavalry group" of General Bolesław Roja.

[5]: 150  Local Jewish communists organized a rally in the city, tore Polish emblems and flags from buildings, and the newly appointed revolutionary committee leader, member of Poale Zion, announced to local wealthy Poles and Jews that their property will be taken from them.

[6] The local Polish intelligentsia and prominent religious Jews, along with the rabbi, were subjected to forced labour in the city.

During the invasion of Poland, which started World War II, on 10 September 1939 German forces reached Ostrołęka.

[8] Under German occupation the town was annexed directly to Germany and in 1940 it was renamed Scharfenwiese to remove traces of Polish origin.

[citation needed] Ostrołęka became a border town, today's easternmost areas belonged to USSR.

The Germans established and operated a court prison, in which they held Poles arrested in the city and county during the Intelligenzaktion.

[13] In December 1940, German police expelled around 1,150 Poles from Ostrołęka and Wojciechowice (present-day district of Ostrołęka), who were transported in trucks to a camp in Działdowo and then deported to the Krakow and Radom districts of to the General Government, while their houses were handed over to German colonists as part of the Lebensraum policy.

[15] The German occupation ended in September 1944, and the city was restored to Poland, although with a Soviet-installed communist regime, which then stayed in power until the Fall of Communism in the 1980s.

A plan created by communist authorities, which allowed for an improvement of the economic situation in Poland, gave Ostrołęka a chance for redevelopment.

The factory Future went bankrupt but small service establishments were opened for average people to invest their money.