William Neil Dennison was a highly decorated artillery

Field Artillery in the American Civil War

Field artillery in the American Civil War refers to the important artillery weapons, equipment, and practices used by the Artillery branch to support the infantry and cavalry forces in the field. It does not include siege artillery, use of artillery in fixed fortifications, or coastal or naval...

 officer

Officer (armed forces)

An officer is a member of an armed force or uniformed service who holds a position of authority. Commissioned officers derive authority directly from a sovereign power and, as such, hold a commission charging them with the duties and responsibilities of a specific office or position...

 during the American Civil War

American Civil War

The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...

, an attorney and business speculator during the postbellum years.

Early life

Born in Ohio

Ohio

Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...

, "Neil" was the son of Ohio Governor and Postmaster General of the United States William Dennison, Jr. and Anne (Neil) Dennison.

Civil War

At the outbreak of hostilities, his father served as the Governor of Ohio (1860–1862), and undoubtedly influenced Dennison's direct commission into the regular U.S. Army

Regular Army

The Regular Army of the United States was and is the successor to the Continental Army as the country's permanent, professional military establishment. Even in modern times the professional core of the United States Army continues to be called the Regular Army...

, on August 5, 1861. He was assigned to the 2nd U.S. Artillery, an organization whose officers corps produced both Chiefs of Artillery for the Army of the Potomac, and the who formed the backbone of the famed U.S. Horse Artillery Brigade

U.S. Horse Artillery Brigade

The Horse Artillery Brigade of the Army of the Potomac was a brigade of various batteries of horse artillery during the American Civil War.Made up almost entirely of individual, company-strength batteries from the Regular Army’s five artillery regiments, the Horse Artillery operated under the...

.

Promoted to first lieutenant on November 12, 1861, Dennison served with the 2nd Artillery throughout the Civil War, almost entirely with the Horse Artillery Brigade. He gained most of his experience while serving as a section chief in Battery A, 2nd U.S. Artillery

Battery A, 2nd U.S. Artillery

For this article, “Company A” and “Battery A” are interchangeable. A battery of four to six cannons, with two to three two-cannon sections was the basic unit of the artillery branch. The organization was commanded by a captain with first and second lieutenants as section chiefs and chief of...

, under the command of Captain John C. Tidball

John C. Tidball

John Caldwell Tidball was a career military officer, noted for his service in the horse artillery in the cavalry in the Union Army during the American Civil War...

. During the Peninsula Campaign

Peninsula Campaign

The Peninsula Campaign of the American Civil War was a major Union operation launched in southeastern Virginia from March through July 1862, the first large-scale offensive in the Eastern Theater. The operation, commanded by Maj. Gen. George B...

, Dennison commanded the rear (left) section of Tidball’s “flying battery.” In 1864, Dennison commanded Battery G, and eventually returned to command Battery A until the end of the war. He was awarded two brevet promotions

Brevet (military)

In many of the world's military establishments, brevet referred to a warrant authorizing a commissioned officer to hold a higher rank temporarily, but usually without receiving the pay of that higher rank except when actually serving in that role. An officer so promoted may be referred to as being...

 for gallantry in combat, including the ranks of captain (for actions at Gaines' Mill

Battle of Gaines' Mill

The Battle of Gaines's Mill, sometimes known as the First Battle of Cold Harbor or the Battle of Chickahominy River, took place on June 27, 1862, in Hanover County, Virginia, as the third of the Seven Days Battles of the American Civil War...

 and Malvern Hill

Battle of Malvern Hill

The Battle of Malvern Hill, also known as the Battle of Poindexter's Farm, took place on July 1, 1862, in Henrico County, Virginia, on the seventh and last day of the Seven Days Battles of the American Civil War. Gen. Robert E. Lee launched a series of disjointed assaults on the nearly impregnable...

) and major (for actions at Antietam

Battle of Antietam

The Battle of Antietam , fought on September 17, 1862, near Sharpsburg, Maryland, and Antietam Creek, as part of the Maryland Campaign, was the first major battle in the American Civil War to take place on Northern soil. It was the bloodiest single-day battle in American history, with about 23,000...

). At war's end, he received his final brevet promotion, to lieutenant colonel

Lieutenant Colonel (United States)

In the United States Army, United States Air Force, and United States Marine Corps, a lieutenant colonel is a field grade military officer rank just above the rank of major and just below the rank of colonel. It is equivalent to the naval rank of commander in the other uniformed services.The pay...

, for his overall service and conduct during the war.

Postwar career

Promoted to the permanent rank of captain in 1867, Dennison requested and received a discharge from the army in 1870. He appears to have dabbled in politics, perhaps hoping to follow in his father's successful career as Governor of Ohio and Postmaster General of the United States. His public reputation suffered due to unsavory business dealings with questionable acquaintances, and he lost the 1879 mayoral race in Columbus, Ohio

Columbus, Ohio

Columbus is the capital of and the largest city in the U.S. state of Ohio. The broader metropolitan area encompasses several counties and is the third largest in Ohio behind those of Cleveland and Cincinnati. Columbus is the third largest city in the American Midwest, and the fifteenth largest city...

.

He moved to Denver, Colorado

Denver, Colorado

The City and County of Denver is the capital and the most populous city of the U.S. state of Colorado. Denver is a consolidated city-county, located in the South Platte River Valley on the western edge of the High Plains just east of the Front Range of the Rocky Mountains...

, where he served as a district attorney

District attorney

In many jurisdictions in the United States, a District Attorney is an elected or appointed government official who represents the government in the prosecution of criminal offenses. The district attorney is the highest officeholder in the jurisdiction's legal department and supervises a staff of...

 and also dabbled in speculative mining and saloons. He was plagued with negative press and maintained somewhat of a rogue's reputation. His business partners, Sam and Lou Blonger

Lou Blonger

Lou Blonger , born Louis Herbert Belonger, was a Wild West saloonkeeper, gambling-house owner, and mine speculator, but is best known as the kingpin of an extensive ring of confidence tricksters that operated for more than 25 years in Denver, Colorado...

, also owned gambling houses. Ultimately, he lost his position with the District Attorney's office.

Colonel Dennison was married to Mary Cole (or Catherine) Haldeman (October 20, 1851 - December 15, 1882), the daughter of Edwin Haldeman and Harriet Cole. They had four children. Dennison died December 31, 1904, and was buried in Green Lawn Cemetery, Columbus, Ohio.