In March 1916, the football club of the Polish Legions, soon known as Legia Warsaw, was founded in Kostiuchnówka.

In July 1916, it was the site of the Battle of Kostiuchnówka between the Russian Army and the Polish Legions in the opening phase of the Brusilov Offensive of World War I.

In the interbellum, it was part of newly reborn Poland, within which it was administratively located in the Wołyń Voivodeship.

In 1928, a celebration of the 10th anniversary of Poland's independence was held in Kostiuchnówka with the participation of 3,000 people, and the laying of the Legions' Mound of Glory on the Polska Góra (Polish Hill) began.

[4] A school with a tourist lodge, erected by the Polish Legions Foundation with contributions from veterans, was then opened.