Marsing is a city in Owyhee County, Idaho, United States. The population was 1,031 at the time of the 2010 census. It is part of the Boise metropolitan area.

Owyhee County is a county in the southwestern corner of the U.S. state of Idaho. As of the 2020 census, the population was 11,913. The county seat is Murphy, and its largest city is Homedale. In area it is the second-largest county in Idaho, behind Idaho County.