Hickenlooper was born in the village of Hudson, Ohio, the son of Abigail and Andrew Hickenlooper. He attended Woodward College and Xavier College. When he was nineteen, he entered the office of A. W. Gilbert, then the city surveyor of Cincinnati, and thoroughly mastered the duties of the position. Three years later, he became the city surveyor himself. After spending two years in this position, the Civil War broke out. He was married to Maria Lloyd Smith and had two children.
Although he was only twenty-four, he recruited what was known as Hickenlooper's Battery or the 5th Ohio Independent Battery, and joined Maj. Gen. John C. Fremont at Jefferson City, Missouri. In 1862, his battery was made a part of the Army of the Tennessee and took a distinguished part in the Battle of Shiloh. Hickenlooper managed to save four of his six guns after the initial Confederate attack. He later defended the famous Hornet's Nest in support of Benjamin M. Prentiss's division. For gallantry at Shiloh, he became commandant of artillery in Thomas J. McKean's division and later chief of staff of the XVII Corps. During the Vicksburg Campaign, Brig. Gen. James McPherson wrote to Secretary of WarEdwin Stanton that, as Hickenlooper's further promotion in the line of the artillery service was impossible, that he be given special consideration for promotion. Hickenlooper served through the Atlanta campaign as an engineer with distinguished honor and participated in Sherman's March to the Sea, and the advance through the Carolinas. He was endorsed for brigadier general by Generals William Sherman, Oliver O. Howard, and Ulysses S. Grant. On January 13, 1866 President Andrew Johnson nominated Hickenlooper for appointment to the grade of brevet brigadier general of volunteers, to rank from March 13, 1865 and the United States Senate confirmed the appointment on March 12, 1866.
Civilian career
After the war, Hickenlooper was appointed United States marshal for the Southern district of Ohio. Then he served two terms as city civil engineer. While in this office, he was made assistant to W.W. Scarborough, then the president of the Cincinnati Gas Company, with the title of vice president. He served as vice president but for a short time, as he was then elected president of the company. He published two books, Competition in the Manufacture and Delivery of Gas, and Incandescent Electric Lights for Street Illumination.He became active in veterans affairs, particularly those of the Society of the Army of the Tennessee, serving as its Corresponding Secretary, where he worked tirelessly for the erection of monuments to the memory of his friend and mentor, General James B. McPherson
