The beginnings of Ciechanowiec date back to the 12th-13th century, when a fortified trading settlement developed around a stronghold located in the area of the present-day town. The first historical records of Ciechanowiec come from the 13th century. In the early Middle Ages, the town was situated on the eastern fringes of Piast Poland and was passing  together with the borderlands from the hands of Polish dukes to those of Russian ones. In the 14 century, it became the property of Lithuanian dukes. The stronghold and the settlement were destroyed during the Tatar invasion in 1241. Conveniently located on a trade route leading to Lithuania and having a great strategic importance, the town was soon rebuilt. In the late 14th century, which saw increased settlement in the region of Podlasie, Ciechanowiec started to evolve into a local centre of trade and crafts, situated in the neighbourhood of one of the most important trade routes leading from Warsaw in the direction of Bielsk Podlaski, Grodno and Vilnius. Ciechanowiec must have had a defensive castle already at that time.

In the first quarter of the 15th century or – according to some sources – in 1429, Ciechanowiec was granted a charter under the Magdeburg law, most probably by Duke Janusz I the Great of Mazovia or Duke Vytautas of Lithuania, as confirmed by the oldest retained records dating back to 1434. By 1446 Ciechanowiec had already had  a Roman-Catholic parish. The first synagogue and Beth Midrash were constructed most probably also in the 14th century [1.1].

During the next two centuries, Ciechanowiec saw its heyday. In the 15th, 16th and the first half of the 17th century, it developed in economic and demographic terms, transforming into one of the major centres of trade, crafts and administration in Podlasie. In the 16th century, thanks to the then owners of the town, the Kiszki family, Ciechanowiec became an important centre of Arianism. The family constructed a castle by the left bank of the Nurzec River. Destroyed during the Swedish Wars, only its foundations and moat have been preserved until today.

Ciechanowiec was damaged during the Second Northern War waged from 1655 to 1660, but soon thereafter the new owner of the town, Idzi Brehmer, and later his wife, took efforts to rebuild the town. In the first years of the next Northern War in the years 1701-1706, Ciechanowiec was once again destroyed by the Swedish troops, which burnt almost all buildings in the left-bank part of the town. The successive owners of the town significantly contributed to its development in the 17th century; the Jabłonowski and Ossoliński families rebuilt and revived Ciechanowiec. In 1739 a foundation of Franiszek Maksymilian Ossoliński financed the construction of a new brick Holy Trinity church and a hospital of the Sisters of Mercy. In 1755 Ciechanowiec was ravaged by a fire. In the late 18th century, in turn, it was severely damaged during the Polish-Russian War and the Kościuszko Uprising. After the third partition of Poland, from 1796 to 1806, Ciechanowiec and most of the region of Podlasie were part of New East Russia. After the Congress of Vienna in 1915, Ciechanowiec was divided into two separate parts: the left-bank Old Town, which was incorporated into the Russian Empire (the so-called Russian Side), and the New Town, situated by the left bank of the Nurzec River, which became part of the Kingdom of Poland (the so-called Polish Side). In 1870, the New Town lost its municipal rights under a decree of Tzar Alexander II and was transformed into a settlement.

Throughout the 19th century, Ciechanowiec experienced a period of relative prosperity. Settlers from Germany contributed to the development of the local weaving and textile industries. The town organised also famous horse fairs. Before the First World War, both parts of the town were inhabited by about 15,000 residents. Ciechanowiec had about 100 industrial plants and about 300 shops run mainly by Jews |[[urle:http://www.ciechanowiec.pl/index.php?option=com_content&task=view&id=111&Itemid=100#top_s]].

The First World War, as well as the Polish-Bolshevik War, took a heavy toll on the town in terms of human death and material losses. About 65% of all buildings in Ciechanowiec were destroyed during the hostilities in August 1920, when units of the Polish army clashed in the area of the town with the Red Army approaching Warsaw. By the end of the war, the population of Ciechanowiec decreased below 5,000 residents.

In the interwar period, Ciechanowiec was a local centre of trade and crafts, inhabited mostly by Christians and Jews. Its infrastructure was gradually rebuilt and modernised. In 1938, the left-bank and the right-bank part were again merged into one administrative body. Ciechanowiec was also an important political centre with cells of the National Party and the “Piast” Polish Peasant Party as well as numerous Jewish parties and political organisations, mostly Zionist and leftist ones. In the second half of the 1930s, the town was a scene of numerous anti-Jewish incidents, which culminated in pogroms in the nearby towns of Przytyk and Wysokie Mazowieckie in 1937.

After the outbreak of the Second World War, in September 1939, Ciechanowiec was occupied by the Red Army. In June 1941, it was invaded by the Germans. In the autumn of 1942, they established a ghetto, to which Jews from Czyżew and Zaręba were deported in late 1941. In October 1942, about 300 Jews from the ghetto were killed in a mass execution near the town.  The liquidation of the ghetto started in early November 1942. Most inhabitants were sent to the death camp in Treblinka. The left-bank part of the town was liberated in early August 1944 and the right-bank part on 13 August. In the years 1944 – 46, Jews were assaulted on various occasions. Severel of them were killed, including Chawa and Meir Kosower, who died on 27 August 1945.

In the wake of the war, the number of inhabitants in Ciechanowiec decreased to about 2,000 people. Moreover, 85% of the town buildings were destroyed. The damaged and depopulated town gradually revived. In 1944, a trade and food company under the name “Jedność” and a gymnasium were set up. In 1946, other enterprises started to operate, including a slaughterhouse and batching plant. Horse fairs started to be organised anew.  In 1951, a sanitary airport was built. In 1956, the Municipal Hospital was established in the building of a hospital for the poor. In 1964, the Museum of Agriculture was moved to the rebuilt Starzeński Palace. It has been one of the most popular landmarks together with an open-air museum.