Minnesota Votes: Election Returns by County for Presidents, Senators, Congressmen, and Governors, 1857-1977.
Swift's vote totals were corrected in the above source. He originally was listed as having 16,937 votes.
"Although three men won this election, which was held before Minnesota was actually a state, only two representatives from Minnesota were allowed in the congressional bill creating the state in 1858. George L. Becker lost in the drawing of lots to decide who would present their credentials, therefore he did not serve in Congress."
from Minnesota Votes: Election Returns by County for Presidents, Senators, Congressmen, and Governors, 1857-1977. p. 65.
The election was held on 10/13/1857. Phelps and Cavanaugh took their seats on 5/22/1858.