Lyon County was one of the nine original counties created in 1861. It was named after Nathaniel Lyon, the first Union General to be killed in the Civil War. Its first County Seat was established at Dayton on November 29, 1861, which had just changed its name from Nevada City in 1862, and which had been called Chinatown before that. After the Dayton Court House burned down in 1909, the seat was moved to Yerington in 1911. There were stories that it was named for Captain Robert Lyon, a survivor of the Pyramid Lake War in 1860, but Nevada State Archives staff discovered a county seal with the picture of the Civil War general, settling the conflict.
The Central Pacific (the first transcontinental railroad) ran through the county, although a portion of the original route has been shifted for a new route south of Wadsworth in favor of Fernley. The Central Pacific later became the Southern Pacific Railroad which was merged into Union Pacific in 1996.
The narrow-gauge Carson and Colorado Railroad had its terminus in Mound House, where it intersected with the V&T. It traveled east through Dayton, then turned south to the Mason Valley, and east again on its way to Walker Lake. Later a branch line connected the C&C to the Southern Pacific at Hazen.
The Eagle Salt Works Railroad ran for 13.5 miles, primarily on the original Central Pacific grade from Luva (2 miles east of Fernley) to Eagle Salt Works.
The Nevada Copper Belt Railroad ran on the west side of the Mason Valley.