Nathaniel Riddell, the son of Fountain and Louisa Riddell, was born in Burlington on 17 July 1872. He grew up in Burlington, where he attended the Morgan Academy. He followed in his father's footsteps and attended Cincinnati Law School, earning a law degree in 1895. He began his law practice in the office of Boone County Judge John M. Lassing. Riddell worked with Lassing for several years.
In 1900, Nathaniel Riddell married Katie L. Huey, daughter of W. S. Huey. In fall 1905 Riddell announced plans to seek political office, running for county attorney. Riddell won re-election in 1908 and served as county attorney until March 1919, when Boone County Judge Perry E. Cason died suddenly. Riddell was selected by Governor A. O. Stanley to complete Judge Cason's unexpired term as county judge1).
Nathaniel was vice president of the Boone County Deposit Bank, and was elected president on the death of his father, Fountain Riddell. Later the bank merged with Peoples Deposit Bank, and Riddell became president of the merged banks on 1 June 1930. Riddell was also president of the Boone County Consolidated Telephone Company, where he was a partner with Judge Lassing and former congressman Arthur Rouse. Nathaniel also branched out into the newspaper business when he bought and operated the Boone County Recorder for several years.
Nathaniel Riddell was still serving as county judge when he died 20 November 1938. He was buried in Highland Cemetery.