JOHN CAVANAUGH was one of three brothers who served with the Camden Fire Department at one time or another during the 1800s. Older brother Benjamin Cavanaugh and younger brother Joseph Cavanaugh been members of the department in the 1870s and early 1880s. 

John Cavanaugh was born in Pennsylavania in 1845 to Matthew and Elizabeth Cavanaugh. The Cavanaughs had started their family in Canada, where older brother Benjamin Cavanaugh was born in March of 1843. The 1850 Census indicates that the Cavanaughs had relocated to Pennsylvania, where sister Sarah was born, before coming over to New Jersey. Sister Mary Cavanaugh was born in 1849. The 1850 Census shows the family living in Camden's South Ward. Two more children had been born, sons Joseph and Matthew Jr., were born in the early 1850s. The 1860 Census shows the family still living in Camden's South Ward.

When the Civil War came, older brother Benjamin Cavanaugh enlisted in the Union Army in April of 1861, serving with Company G, Fourth Infantry Regiment New Jersey Militia, a three-months service unit. Several men who served with the Fourth Infantry became members of the Camden Fire Department after it was founded in 1869, including William W. Mines, J. Kelly Brown, Henry F. Surault, Edward Mead, William Cox, James M. Lane, William Gleason, Theodore A. Zimmerman, Charles G. Zimmerman, William C. Lee, George B. Anderson, Jesse Chew, William H.H. Clark, Cornelius M. Brown, John J. Brown, Benjamin Connelly, and G. Rudolph Tenner. Several other Fourth Infantry veterans played significant roles in Camden in the ensuing years.

John Cavanaugh went to war in 1864. He enlisted as a Private on February 23, 1864 in Company H, 4th New Jersey Infantry Regiment. He served alongside Christopher Mines Jr. who would marry John Cavanaugh's sister Mary after the war.

The Fourth New Jersey had gone into service in the summer of 1861 and had seen considerable service prior to John Cavanaugh's enlistment. When spring came, the regiment left winter quarters to confront the enemy once again. At the Bbttle of the Wilderness the First, Fourth and Tenth New Jersey regiments, lying on the left, were several times attacked with great ferocity by  the Confederates, but at nightfall still held substantially the ground occupied by them in the morning- a heavy assault by the Confederate General Gordon just at dusk being repulsed with heroic gallantry. Among the wounded in that engagement was Lieutenant Colonel Van Syckel of the 4th. At the battle of Spottsylvania the regiment participated in the charge upon the "bloody angle," winning its share of the glory and sustaining its share of casualties. During the first eleven days of Grant's campaign against Richmond the regiment lost 26 killed, 126 wounded and 42 missing. The 4th fought at the North Anna river, Hanover Court House, Totopotomoy Creek, Cold Harbor, Weldon Railroad, Snicker's Gap, Strasburg, Winchester and Charlestown. At the battle of the Opequan the Fourth was with the troops that pressed forward, swept up the opposite hill and forced back the Confederate line, obtaining permanent possession of the hill and holding it, though constantly exposed to a fire which inflicted severe loss, the 4th having 2 killed, 18 wounded and 1 missing. At Fisher's Hill a private of the Fourth named Beach compelled a Confederate lieutenant colonel to surrender his sword, and there were other instances of daring no less noteworthy. 

The regiment fought at Petersburg on January 9, 1865. John Cavanaugh and Christopher Mines Jr. were both promoted to Full Corporal on March 6, 1865. They took part in one last engagement at Petersburg on April 2. After Lee's surrender the regiment was assigned to what was known as the provisional corps, Army of the Potomac, until mustered out on July 9, 1865. The total strength of the regiment was 2,036, and it lost during service 29 by resignation, 319 by discharge, 83 by promotion, 81 by transfer, 257 by death, 372 by desertion, 3 by dismissal, 109 not accounted for, mustered out 783.

Corporal Cavanaugh was among those who mustered out of Company H, 4th New Jersey Infantry on July 9, 1865 at Hall's Hill. 

If they hadn't already been involved before going into the Army, brother Benjamin Cavanaugh and several of his companions became involved in volunteer firefighting in Camden after their return, and it is possible that John Cavanaugh also took part. 

When the census was taken in 1870, Matthew Cavanaugh Sr. had passed away. Mary Cavanaugh had married Christopher Mines Jr., who would go on to a long and distinguished career in Camden politics and government. Mines' brother, William W. Mines, was an Assistant Fire Marshal with the Camden Fire Department, and had served with Benjamin Cavanaugh during the Civil War. He may well have been instrumental in securing Benjamin Cavanaugh's appointment to the Fire Department. Cavanaugh's widowed mother, Mary Cavanaugh, with her sons John and Matthew, lived with Christopher and Mary Mines Jr., and their 10-month old son, Marcus K. Mines, according to the census sheet, which was taken by J. Kelly Brown, another Civil War comrade AND member of the Camden Fire Department. (Note: As of March 1, 2011, Joseph and Benjamin Cavanaugh's 1870 census records have not been located- PMC).

City Directories show that John Cavanaugh lived at 265 Pine Street, the home of his brother-in-law Christopher Mines Jr., in 1878. When the 1880 Census was taken, John Cavanaugh had moved out of the Mines' home at 265 Pine Street and brother Benjamin Cavanaugh had moved in. The Census shows that Elizabeth Cavanaugh and Joseph Cavanaugh were still living there, and that Joseph Cavanaugh was at that time laid up with a broken leg. The 1882-1883 Directory states that John Cavanuagh was boarding at 709 South 3rd Street. He moved back to his brother-in-law's home at 265 Pine Street in 1883 and was still at that address in 1888. The 1890 Veterans census shows him still residing at 265 Pine Street. He was still at that address when the 1892-1893 Camden City Directory was compiled.

John Cavanaugh was appointed to the Fire Department in July of 1890 as an extra man. He did not serve for very long, however. John Cavanaugh passed away on March 6, 1893 and was buried at Harleigh Cemetery.