The oldest traces of settlement in the area of Przasnysz come from the turn of the Bronze and Iron Age. In the 13th century in Przasnysz, on the Węgierka River, there was a market settlement. There was also a hunting court of the Mazovian princes, described by Henryk Sienkiewicz in Krzyżacy. The name of the city according to folk sources comes from the millerPrzaśnik, who hosted the stray hunting Prince Konrad I of Mazovia and was then knighted with the surrounding lands. Przasnysz's rapid development was due to its favorable location on the border between two economically important areas - the Kurpiowska Plain and the agricultural Ciechanowska Upland. On October 10, 1427, Przasnysz obtained the town privilege under the Chełmno law from the Masovian prince Janusz I the Elder. The city flourished in the 16th century, especially after the incorporation of Mazovia into the Crown in 1526. Administratively Przasnysz was part of the Ciechanów District as the capital of a vast powiat. In 1576, Przasnysz became the seat of the non-castle eldership. In 1648, the Przasnysz eldership was awarded to the defender of Zbaraż, Prince Jeremi Wiśniowiecki.
During World War I, in November and December 1914, heavy fighting took place near Przasnysz between the Russian and German armies. The city changed hands many times. February 24, 1915 was taken by the Germans, but on February 27 they were forced out by Russian troops from the First and Second Siberian Corps.
In August 1920, extremely fierce battles with the Bolshevik 15 Army took place near Przasnysz. For two weeks the city was occupied by the Soviet army. On August 21, 202 Liberation was brought by Przasnysz Infantry Regiment from the Volunteer Division of Colonel Adam Koc. In the interwar period, Przasnysz was the capital of the poviat in the Warsaw Province. In the first years of independence, reconstruction from war damage continued. Many public buildings were built: power plant, junior high school and elementary school, agricultural school, city theater, stadium and sports house. The main occupation of the inhabitants of Przasnysz was still agriculture, craft and small trade. In 1938, Przasnysz had 8,000 residents, including approx. 3 thousand Jews. In the first days of September 1939 near Przasnysz, the Mazowiecka Cavalry Brigade fought hard, under the command of Colonel Jan Karcz. After the September defeat, the Germans joined the Przasnysz District to the Reich.
Shortly after the Soviet army seized the city on January 18, 1945, the NKVD began mass arrests and deportations of Polish patriots. In the years 1945–1951, numerous armed units of the anti-communist underground operated near Przasnysz. In the 1960s, the rapid development of the city began, slowed as a result of the administrative reform of 1975. In 1966, a branch of Zakład Aparatury Gospodarcza im. Georgi Dimitrov, where lightning arrestors were produced. For the needs of this plant, a school complex was established to house a vocational school and technical college. Since January 1, 1999, Przasnysz is the seat of the county in the Masovian Voivodeship.
The coat of arms of Przasnysz depicts a defensive wall made of red brick on a silvershield, with three such towers of equal height. Each tower is covered with a conical red roof. Each tower has an entrance gate and one soaring hole above it, both black. Heraldic shield border black. The heraldic image dates from the 16th century.
