Serock [ˈsɛrɔt͡sk] is a town at the north bank of the Zegrze lake in the Legionowo County, Masovian Voivodeship, Poland, around 40 kilometres (25 miles) north of Warsaw. It has 4,109 inhabitants (2013).

The stronghold was founded in the 10th century, shortly after the creation of the Polish state by the Piast dynasty. The first mention of the settlement dates from 1065 with the so-called "Falsyfikat mogileński," a document from the Benedictine monastery in Mogilno. The town is situated on the route which was the trade route leading from Gdańsk and Truso to Rus'.

Between 1113 and 1124, Serock was also mentioned in a list as one of the most important princely castles of Mazovia, which operated a river crossing (the Bug and Narew rivers intersect beside Serock) with a customs house.

During the fragmentation of Poland into smaller provincial duchies, Serock became part of the Duchy of Masovia, still ruled by the founding Piast dynasty. In 1417, Serock was granted town rights under Chełmno law by Janusz I of Warsaw. By then it was already a craft and commercial center. From this period the urban layout was created in the form of the market square and the late Gothic church of the parish.

Serock was a royal town of the Polish Crown, administratively located in the Masovian Voivodeship in the Greater Poland Province. In the 15th and 17th century municipal courts were held there. From 1655 to 1660, during the Swedish invasion, the town was largely destroyed. After the Third Partition of Poland in 1795, it was located in the Prussian Partition. In 1807 it came under the possession of the short-lived Polish Duchy of Warsaw, and after its dissolution in 1815 it was part of so-called Congress Poland in the Russian Partition of Poland.

Serock repeatedly was on the battle lines on the outskirts of Warsaw, including in 1794, 1809 and 1831. In 1806, on the orders of Napoleon I fortifications were built in Serock. From 1807 it was a fortress. During the Polish–Austrian war in 1809, it was the operational location of General Józef Niemojewski's troops. Then the fortress was expanded (at the initiative of the French Marshal Davout) until 1811, when it gained greater importance than Modlin Fortress. In 1831 the Polish army formed in Serock (during the November Uprising).

After the unsuccessful Polish January Uprising, Serock was deprived of town rights by the Russian administration in 1870, and entered a period of stagnation. Serock experienced a sizeable influx of Jews as a result of Russian discriminatory policies and the expulsion of Jews from Russian lands (see Pale of Settlement), however, many soon emigrated to the Americas. In the early 20th century Serock was a popular destination for Polish artists. During World War I it was occupied by Germany, and in 1918 local Poles disarmed the Germans, and Serock was reintegrated with Poland, which just regained independence. During the Polish–Soviet War, in 1920, the town was briefly occupied by the Soviet Russians, who destroyed the local Jewish library. The town rights were eventually restored in 1923.

In September 1939, Serock was a place of fighting between the Poles and the invading Germans during the Invasion of Poland, which started World War II. On September 5, 1939, around 50–70 people, both inhabitants of Serock and refugees from nearby Nasielsk, were killed in a German air raid. In mid-September 1939, the Einsatzgruppe V entered the town to commit atrocities against the population.