The future Port of Kokura became the starting point for a highway that led to other Kyushu towns, and the town flourished. New landscaped gardens and ponds appeared around the castle.
The castle's keep was caught fire in 1837, and it was rebuilt two years later. In the mid-1800 when the Tokugawa Shogunate began to fade, the Port of Kokura area became the main base for attacks on the Choshu clan. Then in 1866, the castle was burned and abandoned when the Battle of Shochuseito forced the Ogasawara to leave the Port of Kokura.
During the Satsuma Rebellion in 1877, a regiment of infantry was stationed at the Port of Kokura from which they went to war. Later, the 12th infantry brigade was stationed there. The Port of Kokura won status as a municipality in 1900. Throughout its history, the Port of Kokura continued to be a focal point for trade and commerce, although it was never considered a major Japanese port.
In 1945, the Port of Kokura was the first target for the United States' atomic " Fat Man " bomb that instead struck the secondary target of Nagasaki . On the morning of that ill-fated air raid, the Port of Kokura was covered by clouds and smoke. Mission commander Major Charles Sweeney could only drop the bomb if he could see the target. Since he could not see the Port of Kokura, he was order to go on to Nagasaki. Since that day, the Japanese refer to the "luck of Kokura." The Port of Kokura had also been the secondary target for the bomb dropped on Hiroshima just three days earlier.
After World War II, Kokura Castle was requisitioned by the United States, but it was returned to the people of the Port of Kokura in 1957. By 1959, the citizens had rebuilt the castle.
In 1963, the Port of Kokura municipality was dissolved when it was merged, with four nearby cities, to form the new Kitakyushu City.