On 28 November 1900, he married Clara Matilda Borg in Porter County, Indiana. M. J. Lonner was the officiating minister. Clara's sister Malinda A. Borg married Charles August Lawrence on the same day. Clara was thirteen years older than Nels, and was 42 years old when they married. The couple never had biological children, but they raised an adopted daughter and son. The girl was born Etta Maria Carter, but was listed as Etta Samuelson, adopted, in the 1910 United States Census. The boy, Leroy G. "Roy" Johnson, had joined the family by 1920; he was listed as a lodger in the Samuelson home in the 1920 United States Census.
Nels' older brother John Samuelson committed suicide by hanging on 9 July 1929. John's daughter Anna was enumerated in Nels and Clara's household in the 1930 United States Census. Clara died at the Samuelson home in Baileytown, Porter County, Indiana on 18 March 1934.
On 29 June 1935, Nels was cultivating corn on his farm. When his team of horses became frightened, Nels was dragged under the blades of the cultivator and was killed. His memorial service was held at the Augsburg Lutheran Church, and he was buried in Augsburg Lutheran Church Cemetery on 2 July 1935.
Vidette-Messenger, 1 July 1935, page 1
Vidette-Messenger, 3 July 1935, page 4