WILLIAM C. HORNER was born in Stockton Township, what is now Camden, New Jersey in 1869. He was the son of Lemuel D. Horner Sr. and his wife, the former Emma Louise Carter. The Horners had come to the area around 1795 and at one time owned a large farm north and west of what is now Westfield Avenue, with land in both present-day Camden and Pensauken Township. Lemuel Avenue in East Camden is named after Lemuel D. Horner. William Horner was the second of six children, coming after sister Anna Horner. William was followed by Minnie Horner, Lemuel H. Horner, John Morgan Horner, and Emma Horner. 

William C. Horner married Mary S. Beideman on July 6, 1892 at Tabernacle Methodist Episcopal Church in Camden, New Jersey. She was the daughter of Rebecca and Benjamin C. Beideman, who owned a large farm at the corner of North 35th Street and River Avenue. Beideman Avenue was named after the Beideman family, who had much property in the immediate area. Daughter Adalisa Horner was born in June of 1893, son Russell E. Horner arrived in July of 1894. Another son, Melvin B. Horner, was born in 1895, but died at the age of two months. A final child, Benjamin B. Horner followed in 1901. 

The 1896 City Directory shows William C. Horner, fireman, at the corner of North 36th Street and Rosedale Avenue. The 1898 edition shows him as a butcher, at 322 North 36th Street. William C. Horner and brothers Lemuel and John were all members of the Third Infantry Regiment, New Jersey National Guard and all served during the Spanish-American War. William C. Horner was discharged from service in December of 1898 and returned home to his wife and children. In the spring of 1899, the Town of Stockton was annexed by the City of Camden, bringing what is now known as Cramer Hill and East Camden into the city. Stockton's police were disbanded and new policemen were appointed. One of the first of the new policemen was William C. Horner. He was promoted to Sergeant on September 25, 1899.

By the summer of 1900 William C. Horner had moved to 308 North 36th Street. Tragically, Russell Horner drowned on June 22, 1908 while swimming in the Delaware River. The Horners stayed at the North 36th Street address into 1911. In 1912, Mary Horner's widowed mother, Rebecca Beideman passed away, and the Horners moved into the Beideman farmstead at 3517 River Avenue where they remained through 1914. The family moved to 116 North 34th Street in 1915, and 226 North 32nd Street in 1916. City Directories from 1917 and 1918 have William C. Horner and family residing at 4006 Westfield Avenue. 

The 1920 Census shows William and Mary Horner at 4013 Westfield Avenue. This appears to be a duplex, and the other unit at the address was occupied by the Horner's daughter Adalisa Horner Starkey, her husband Edward and their children. In 1921 William Horner and family moved to 227 North 42nd Street, where they lived to at least 1931.

Sergeant Horner had served as acting Captain of the of the Third Police District, all territory north of the Cooper River on occasion early in his career. In June of 1927 he was put in charge of the district once again, and held the post as late as August of 1931. He was put in charge of the police department's missing persons bureau in the fall of 1931, then made desk sergeant at police headquarters in December of that year. After several months of booking prisoners, Sergeant William C. Horner put in for his pension, which was granted effective September 15, 1932

By November 16, 1934 William and Mary Horner had moved to 2129 43rd Street in Pennsauken, just over the Camden-Pennsauken border. Their son Benjamin B. Horner remained at the North 42nd Street address until his death in 1952. William C. Horner passed away at home on February 14, 1943 and was buried at Bethel Cemetery in Pennsauken. His wife joined him on June 17, 1948