Samuel Danford Nicholson (1859 – March 24, 1923) was a United States senator from Colorado.

Nicholson was born on Feb. 22, 1859 in Springfield, Prince Edward Island, British North America, he attended the public schools there and moved to Michigan and then to Nebraska and later, in 1881, to Leadville, Colorado.

He discovered the zinc ore that bears his name, Nicholsonite.

From 1893 to 1897, Nicholson was the Populist mayor of Leadville; he moved to Denver in 1902.

During the First World War, he served as State chairman of the Liberty Loan and Victory loan campaigns, and was a member of the United States Fuel Administration.