Legendary origins According to family legend, the Kossakowski family traced their origins back to a
Roman soldier named Valerius, who, during one of his battles, had a raven land on his helmet and assist him in combat. Hence his nickname,
Corvus (the raven). His descendants were said to have arrived in Poland via
Hungary.
Stanisław Kazimierz Kossakowski (1837–1905), the family historian, identified Gopta Primus Gothorum Heros, who lived around the year 440, as the progenitor of the family. Valerius, according to him, was believed to be his descendant.
Origins in Mazovia The Kossakowski family was first recorded in the 13th century in the
Ciechanów Land. In 1224,
Konrad I of Masovia granted land to one of his army commanders, Wawrzęta/Wawrzyniec Korwin. In the 14th and 15th centuries, the Kossakowski family appeared in the
Łomża Land, where they established several noble villages named Kossaki. The family gained particular prominence through the sons of Mroczek of Kossaki, Mikołaj Jakub and Stanisław Wojciech, who held official positions in the
Wizna Land. They became the progenitors of the two most significant branches of the family.
Lithuanian branch The great-grandsons of Mikołaj Jakub Kossakowski, Franciszek Nikodem and Mikołaj, were the first members of the family to attain the office of starosta, successively becoming starostas of Łomża. distinguished himself in the
Battle of Kircholm, and his son settled in the
Grand Duchy of Lithuania, eventually becoming the castellan of Mścisław. From him descends the Lithuanian magnate branch of the Kossakowski family. The heir to the Lithuanian estates of the family was Jan Eustachy's grandson, Dominik Kossakowski, the founder of the town of Jonava. He had four sons: Michał, who became the
voivode of Vitebsk and
Brasław;
Szymon Marcin, the
Grand Hetman of Lithuania;
Józef Kazimierz, the
bishop of Livonia; and Antoni, castellan of Livonia. Szymon Marcin and Józef Kazimierz were sentenced to death and executed for treason against the fatherland. Antoni established a branch of the family in , and Michał in . At the end of the 18th century, Michał Kossakowski received for the family the title of count, granted by the imperial court in Vienna. The line in Vaitkuškės maintained a high aristocratic status within the
Russian Empire. Successive heirs,
Józef Kossakowski and Stanisław Szczęsny Kossakowski, each left only one son, which helped preserve the estate from significant diminishment. The son of the latter, the heraldist
Stanisław Kazimierz Kossakowski, divided the estate among his three sons; however, it was largely lost due to confiscations following
World War II. ==Coat of arms==