was a Japanese samurai who lived during the transition from the Edo period to the Meiji era. He is best known for his role in the assassination of Ōkubo Toshimichi.
Shimada Ichirō was born to an ashigaru in the Kaga Domain (modern city of Kanazawa), which was later merged to the Ishikawa Prefecture by the Meiji government.
Following the death of Saigō Takamori during the Satsuma Rebellion, a group samurais among his sympathizers formed an antigovernment faction called Sankō-ji, led by Shimada. The faction began plotting the assassination of Kido Takayoshi and Ōkubo Toshimichi to avenge Saigō. However, the passing of Kido on May 26, 1877 shifted the focus solely on Ōkubo.
Shimada along with Chō Tsurahide disappeared from Kanazawa in March 1878, keeping the central government on high alert. Shimada left his family with poetry, setting his motives and coming to terms with his demise.
On May 14, 1878 in Tokyo, Shimada along with six other men, dragged Ōkubo out of a carriage and cut his throat and left the body with their weapons and an explanatory note. Immediately after, they turned themselves in to a nearby palace. All were executed in July of the same year.