The draft 1850 census lists slaves in Salt Lake County and Davis County.
Utah Territorial Census Schedule 2 for Salt Lake County and Davis County, 1851, MS 2672, The Church History Library
1 John H. Redd [owner]
Venus
Chancy
Luke
Marinda
Ama
Sam Franklin Free when twenty-one
Salt Lake Country
2 John H. Bankhead [owner]
Sam
Nancy
Alexander
Thomas
Nathan
Miram
Sam
Rauley
Howard
3 Brigham Young [owner]
Greene
4 Abraham Smoot [owner]
Smoot
5 John Brown [owner]
Betsy
Davis County
William Bams [owner]
Charlotte
Daniel
At the type of the page the word slave is crossed out and replaced with colored.