Ciechanowiec is a Polish town in the podlaskie region.
Before 1429, it was a private town with the Magdeburg law, and it was located in the land of Drohicka in the podlaskie region. The Polish part of Ciechanowiec was a private land in the Congress Kingdom.
Ciechanowiec gained municipal Magdeburg rights in 1429, probably from prince Witold of Lithuania.
In the 16th century, the town was owned by the Kiszka family. In the mid-16th century, Piotr Kiszka – the castellan of Trakai – constructed a castle at the north-east from the town. Between 1617-1642, Mikołaj Kiszka surrounded that castle with earthly fortifications, but shortly afterwards, the castle was burned during the Swedish wars, and the Ossoliński headquarters, which was established at the ashes of the castle, was burned by the people of Russia in 1915.
Between 1736 and 1739, a brick-made church of the Holy Trinity was constructed based on the design of an architect of Warmia – Jan Adrian Kluk. His son, priest Jan Krzysztof Kluk, was devoted to natural science, becoming one of the most important Polish naturalists of the Renaissance period.
During the times of the partitions of Poland, Ciechanowiec was first given to the people of Prussia, and after the Congress of Vienna – it went to the hand of Russia. At that time, the town was divided into two parts. The right-bank part was situated within the borders of the Polish kingdom, while the left-bank Old Town was located in Russia. In the late 19th century, the textile industry was developing in the town. Ciechanowiec was also famous for its horse markets.