JOHN PETER DECKER was born March 13, 1841 in Newfoundland, New Jersey, which is in Morris County, to Peter Mark Decker and his wife the former Maria Blauvelt. His mother  died in 1848. When the Civil War began John P. Decker answered his country's call on April 12, 1861 when he enlisted in the First New Jersey Volunteer Infantry. He saw action at the First Battle of the Bull Run, then mustered out on July 13, 1861. He reenlisted in 1862 at Newark, New Jersey, serving with the Thirteenth New Jersey Infantry, with whom he served until the war ended. John P. Decker re-enlisted in Company D, New Jersey 13th Infantry Regiment on  August 25, 1862. He was Promoted to Full Sergeant Major on August 31, 1864, and was promoted to Full 2nd Lieutenant on April 24,  1865. Lieutenant Decker mustered out on June 8, 1865 at Washington, DC.

The Thirteenth Mew Jersey was mustered into Federal service on August 25, 1862, and was assigned to the Army of the Potomac's XII Corps.

Despite being in existence for less than a month, and with bare rudimentary military training, it was thrown into a combat role at the September 17, 1862, Battle of Antietam. There it fought near the Dunkard Church and performed relatively well considering the unit's 

inexperience. Its further service would see the regiment take part in the Battles of Chancellorsville, Gettysburg, the Atlanta Campaign (most notably at the Battle of Peachtree Creek), the March to the Sea, and Bentonville.

John P. Decker married Abigail Sayers in Newark, New Jersey in 1865. The family lived in North Jersey until the mid-1870s, then moved to New York. By 1887 the Decker were living on Staten Island, and had been blessed with five children, Sons Edwin, Charles, Joseph, and Marcus, and a daughter, Grace. 

John P. Decker remained on Staten Island through at least 1910. The 1920 Census shows him and his wife living in Monrovia, California. In 1923 they moved to Camden, New Jersey and took up residence with their youngest son, Marcus F. Decker, who lived with his family in Fairview and worked as a painter. Abigail Decker passed away in 1927.

John P. Decker died at home on June 14, 1931. He was buried in Evergreen Cemetery in Camden. Mr. Decker had been a member of the Thomas M.K. Lee Post No. 5 of the Grand Army of the Republic (G.A.R.)  

John P. Decker's grandson, Edwin V. Decker, son of Marcus Decker, had a long and distinguished career with the Camden Fire Department.