On May 13, 1816, Hanna was elected as one of the forty-three delegates to the 1816 Indiana Constitutional Convention at Corydon, Indiana, where the delegation considered statehood for the Indiana Territory and drafted the state's first constitution. Hanna was one of Franklin County's five representatives, which also included James Noble, who became Indiana's first U.S. Senator after it achieved statehood in 1816. When a state militia was organized in 1817, Hanna served as a brigadier general in its Sixth Brigade, Third Division.