Born in Cincinnati, Dennison graduated from Miami University, studied law, and was admitted to the Ohio bar in 1840. A canny businessman, he led the Exchange Bank and the Columbus and Xenia Railroad, and organized the Columbus and Hocking Valley Railroad, while becoming active in politics. In 1840, he married Anne Eliza Neil, the daughter of the wealthy Columbus businessman William Neil, whose farm later became the campus of Ohio State University. Together, William and Anne Dennison had seven children. The eldest of them was a son, William Neil Dennison, who later won distinction in the Civil War while serving in the U.S. Horse Artillery Brigade. William Dennison Jr. was one of the first major Ohio politicians to leave the dying Whig Party for the new Republican Party. He rose quickly through the party ranks due to his anti-slavery and anti-discrimination efforts in the Ohio State Senate. Dennison was elected to the governorship in 1859, defeating Rufus P. Ranney, and served a single term from 1860 to 1862. Before the outbreak of the AmericanCivil War, he refused the demands of Kentucky and Virginia state authorities for the extradition of fugitive slaves or the punishment of those who helped them.
Civil War
He organized Ohio's mobilization in the opening days of the war, and was generally effective, despite having a small staff and no prior military experience. His efforts led to the creation of several large training camps for newly raised troops, one of which would be named for him. Dennison tried but failed to be elected to the United States Senate in 1861, when he was defeated by John Sherman. Without being asked by the War Department, he sent Ohio troops under George McClellan into western Virginia, where they guarded the Wheeling Convention, which eventually led to the admission of West Virginia as a free state. He also took the initiative to seize control of Ohio's railroads and telegraph lines early in the war to allow military usage, angering Peace Democrats in the Ohio Legislature. He denounced secession and Ohio's "Copperheads", established a consistent supply of arms and equipment for the new troops, and was a vocal supporter of Lincoln's policies. During his term, he raised over 100,000 troops and organized 82 three-years regiments for the Union army. However, errors by the Governor and his subordinates led the state's alliance of Republicans and War Democrats to drop Dennison as a candidate in 1862. The parties turned instead to David Tod, a War Democrat. Historian Richard H. Abbott wrote, "No Ohio chief executive had ever exercised such powers and fulfilled such duties with a greater sense of public responsibility and determination. Nevertheless...politics dictated his demise." Dennison accepted this turn of events with good grace, capably advised his successor, and provided valuable services in helping recruit black troops for Ohio units. He served as Chairman of the Republican National Convention in 1864. He was appointed U.S. Postmaster General by PresidentAbraham Lincoln, and served from 1864 to 1866, leaving the Cabinet after he decided he could no longer support the policies of President Andrew Johnson.
Postbellum career and memorialization
After the war, Dennison served on the Columbus City Council and organized the Franklin County Agricultural Society. President Ulysses S. Grant appointed him the first President of the Board of Commissioners for the District of Columbia, the highest governing office of Washington, D.C., in which Dennison served from 1874 to 1878. He sought the Republican nomination for the U.S. Senate in 1880, but was defeated by James Garfield. Dennison remained active in state and national politics until his death. He left behind a widow and seven children, and was buried in Green Lawn Cemetery, Columbus, Ohio. Of Dennison's single term in the opening stages of the Civil War, historian John S. Stilt wrote, "His wisdom and foresight were appreciated by few and condemned by many.... It is doubtful whether any of his predecessors could have met the issues any more successfully." Camp #1 of the Department of Ohio of the Sons of Union Veterans of the Civil War is named for Governor William Dennison. It was chartered August 1, 1882, shortly after Dennison's June 15, 1882 death at age 66. The William Dennison school in Washington, DC, named in his honor, was opened in 1885 on S Street between 13th and 14th Streets, NW. It closed sometime after 1947 and was razed prior to 1985.
