First mentioned in a chronicle of 1100, when it was in possession of Yaroslav the Wise's grandson David of Brest, Dubno was even a seat of local princes for a short period of time. In the early 14th century it was annexed by Poland with the rest of Halych-Volynia. Later, it became a notable royal stronghold guarding that country's eastern border. Granted city rights in 1498, the town attracted many foreign settlers, most notably Jewish and Armenian. As such, it became the seat of one of the oldest and most vibrant Jewish communes in Central-Eastern Europe. Since 14th century owned by the mighty Ostrogski family, who built the Dubno Castle during the times of Konstanty Wasyl Ostrogski (Ostrozhsky). Between 1489 and 1506 the castle was significantly expanded by Konstanty Ostrogski, who made it a modern fortress, one of the strongest in the area.
With the death of Janusz Ostrogski in 1619, the last of his kin, the area was inherited by his brother-in-law Aleksander Zasławski of the cadet branch of the Ostrogski family. About that time it was again modernized to stand up to the standards of renaissance warfare and modernization of artillery. Finally, in 1753 it was sold to the Lubomirskis following the Treaty of Zdołbunów.
In the 1780s the castle underwent yet another modernization and was rebuilt as a residential manor, mostly losing its fortified character. By that time, the town was the largest settlement of the Volhynian Voivodeship and arguably the most notable centre of the area. Annexed by Imperial Russia in 1795 during the Partitions of Poland, the town initially flourished as the szlachta register was moved there from Lwów. However, after the third partition it was moved to Kiev and the town lost its importance, gradually falling into neglect. In 1870 it was declared a Fortified Town, which imposed serious limitations on settlement and housing construction, further limiting the development. However, it remained a notable centre of commerce, most notably because of numerous Czech settlements around the town, that gave it the nickname of the brewery of Volhynia. The castle was ruined in 1915 during the World War I.
Retaken by Poland in 1918 and finally granted to that state in the Peace of Riga, it was a seat of a powiat and a notable military garrison of both the KOP, and the Polish Army, with the 43rd Rifle Regiment (part of the 13th Kresy Infantry Division), and the 2nd Regiment of Mounted Artillery (part of Volhynian Cavalry Brigade) stationed here. Dubno also was the seat of Papal Eastern Seminary (Papieskie Seminarium Wschodnie). In 1935 a large prison was started to be built, the third biggest in Poland at that time. Between 1932 and 1939 the castle was being rebuilt in its original form, but the works were stopped by the outbreak of World War II. In 1937, its population was app. 15,500, out of which Jews made 45%, Ukrainians 29%, and Poles 26%.