Niels Peter Olsen was born on October 12, 1850, in Frendved, Holbaek, Denmark. He was the son of Ole Jorgensen and Magdalene Nielsdr (Nielsen). His siblings were Jorgen Peder, Ellen Magrethe, Christine, Anders Christian, Ellen Margrethe, twins Niels and Peter who died at ages 1 and 1-1/2 yrs, Carl Christian who died at age 6 weeks, and an unnamed male sibling that died at birth.

Niels Peter Olsen married Karen Nielsen in Denmark. It is believed they were married on July 31, 1880, in Skellebjerg, Holbaek, Denmark. They immigrated to the United States in July 1883. His immigration registration record listed his occupation as "Hjulmand," which is a wheelwright. Their last residence was listed as Buerup, Halleby, Holbaek, Denmark.

Their known children were:
Hans Olsen born in Denmark circa 1881 in Denmark
Agnes Olsen born October 6, 1882 in Denmark
Otto Olsen born September 23, 1885
Garfield Olsen born on July 1, 1887
Victor Olsen born May 1, 1889
Harry Olsen born October 27, 1890
Mabel Olsen born December 20, 1892

In February 1884, Niels and his brother, Jorgen, each purchased 40 acres of property in Fairplains Twp, (Montcalm County), Michigan, in the NW Quarter of Section 14, in Twp 9 North of Range 7, West. This now has an address of 8200 Holland Road, Sheridan, Michigan.

Niels died in Fairplains Twp, (Montcalm County) Michigan, on November 11, 1892, five weeks before the birth of their last child, Mabel. Niels died from typhoid fever at the age of 42. On his death certificate his occupation was listed as farmer. After Karen and Niels died, Jorgen inherited their property and helped raise several of the their children.

Niels and Karen Olsen are buried in South Sidney Cemetery in Sheridan, (Montcalm County) Michigan. They are buried in plot 20B, along with their son Victor, and Niels' siblings, Ellen and Jorgen.