SETH DANIEL MONNELL was born in New Jersey on December 15, 1874 to John Monnell and his wife, the former Frances E. Griffin. The family name appears in some records as "Monnell" and in others as "Monell". Camden Fire Department records from 1931 have it as Monnell. In the late 1870s and early 1880s the Monnells lived at 809 Mount Vernon Street, the home of Frances' parents, Seth D. and Margaret Griffin. Besides Set there were three other children in 1880, older sister Maggie, and younger siblings John and Ella. Sisters Amelia and Jane came along in the 1880s. John Monnell worked at different times as a laborer, as a casting cleaner, and as an iron chipper. These seem to indicate that he generally worked around iron foundries and forges. The Monnells appear to have moved to Waterford Township in the mid-1880s. Seth Monnell, however either stayed in Camden with his grandparents or returned in his late teens. The 1894-1895 Camden City Directory lists him at 923 South 8th Street, working as a laborer. The 1895-1896 edition shows him living at 813 Mount Vernon Street, working at the R.D. Wood & Company Iron Works as a laborer. He had wed, and his wife Mattie worked as a dressmaker By 1896 he had found work as a railroad conductor. Seth and Mattie Monnell moved to 1012 South 8th Street prior to the compilation of the 1897 Camden City Directory, and remained at that address into 1899. By the spring of 1900 they had moved, along with Mattie's two daughters from a previous marriage, Hannah and Viola Drummond, to 744 Mount Vernon Street. He styed atthat address through at least 1905.

Seth D. Monnell was appointed to the Camden Fire Department on February 3, 1904. The 1910 Census shows that the Monnell family had moved to 708 Mount Vernon Street. Seth Monnell was still at this address when he registered for the draft in September of 1918. When the census was taken in January of 1920 Seth Monnell had moved to 714 Mount Vernon Street. Sadly, he was now a widower. He was living with his widowed mother-in-law, Mrs. Martha A. Drummond, and stepdaughter Viola. He remarried shortly after the census was taken. The 1924 City Directory has Seth D. Monnell and his wife Laura at 778 Walnut Street. 

When  the 1927 City Directory was compiled Seth Monnell had left Camden and the Camden Fire Department. The 1930 census lists him in Westville, New Jersey. By 1931 he had moved to 52 Jackson Road in Berlin, New Jersey. His older sister Margaret had married Frank Blaese and lived for well over 50 years in Berlin before her passing in 1952.

Seth Monnell died on September 1, 1946 in Philadelphia.