Roop County is a defunct county of Nevada. It was created as Lake County in 1861 as one of the original nine counties of Nevada. The name Lake County was chosen on account of the many lakes in the area, including Honey Lake, Pyramid Lake, and Winnemucca Lake.
In 1862 Lake County was renamed Roop County after Isaac Roop, a Governor of the unofficial Nataqua Territory which had previously existed in the same area. At the time Roop County was created, the border between Nevada and California was poorly defined in Nevada's Organic Act, and much of Roop County, including Susanville, was claimed by California and included in Plumas County, California.The establishment of Lake (later, Roop) County in northwestern Nevada created a boundary dispute with California. This has been called the Roop County War[1], the War of Injunctions, or the Sagebrush War.
This resulted in the appointment of a joint California-Nevada boundary survey, with Surveyor-General J.F. Houghton acting for the State of California and Butler Ives, for the Territory of Nevada. The final surveyors report, accepted by California on April 4, 1864, and by Nevada on February 7, 1865, proved that the Honey Lake area was in California. The California portion of Roop County became Lassen County, California, in 1864. The remainder ceded to Washoe County, Nevada.