It contained Carson City, the county seat, and later, the state capital, founded two years earlier.

It was named after Major William Ormsby, one of the original settlers of Carson City, killed along with seventy-five other men in 1860, in an unsuccessful attempt to subdue a perceived uprising of Paiute people near Pyramid Lake, Nevada, which was at the time part of Utah Territory.

The county's population dwindled significantly after the gold rush days.

Discussions began about merging Carson City with Ormsby County after World War II.

However, the effort never got beyond the planning stages until 1966, when a statewide referendum formally approved the merger.