Bullfrog County was a short-lived county in the U.S. state of Nevada, created by the Nevada Legislature in 1987. It consisted of an uninhabited 144-square-mile (370 km2) area around Yucca Mountain, completely enclosed by southern Nye County, the county from which it was created. Its county seat was located in Carson City, the state capital—270 miles north. Its creation was ruled in violation of the state constitution in 1989. In compliance with the ruling, the legislature dissolved Bullfrog County and retroceded its territory to Nye County. 
Had it still existed, Bullfrog County would be currently the second youngest county in the United States and the only enclave county. As it is, the county is the shortest lived county in United States history, and to present day, the last county to be dissolved.
The county's establishment was a response to plans by the United States federal government to create a disposal site for radioactive waste in Yucca Mountain. The federal government agreed to provide payment-equal-to taxes (PETT) funding to Nye County during the characterization and construction of the Yucca Mountain repository. This money was intended to go straight to Nye County, bypassing the state government. In response, Nevada Assemblyman Paul May introduced AB 756 , a bill declaring the unpopulated area around the proposed nuclear waste site to be a new county, Bullfrog County. Because this new county had no population, any federal payments for placing the nuclear waste site there would go directly to the state treasury. Furthermore, property tax rates in the county were set at 20 percent, the highest allowable by the state constitution. This tax burden (potentially up to $25 million) was meant to discourage the waste site's creation by making it prohibitively expensive to use the land for a radioactive waste dump. However, it also guaranteed that the waste site would at least be profitable for the state government if it were ever built. The bill was passed at 3:45 am on June 18, 1987—near the end of the year's legislative session—and signed into law by Governor Richard Bryan.  The bill stipulated that if the repository was not built in the county, it would be dissolved and reincorporated into Nye County. 
Bullfrog County was the only county in Nevada whose county commissioners and sheriff were not elected. Instead, the law creating the county stipulated that those officials were to be appointed by the governor. It was not assigned to any of the state's nine district courts, and as such had no district attorney or judiciary. 
To date, Bullfrog County is the only county with a population of zero known to have existed in the United States and one of a few counties with a county seat outside its borders ( South Dakota's Oglala Lakota and Todd counties and Virginia counties with seats in (usually adjoining) independent cities also have county seats outside their borders). It contained no paved roads, buildings or infrastructure of any kind.  The easiest ground access to the county was by way of a dirt road off U.S. Route 95. 
More than three-fourths of the county's land was closed to the public. Half of it was taken up by the Nevada Test Site, and a quarter by the Nellis Air Force Range. The remaining fourth was owned by the Bureau of Land Management, but few people visited there. 
The existence of Bullfrog County had the potential to create serious legal problems for the state of Nevada. The Nevada Constitution requires all criminal trials to be tried in the county where the crime occurred, and before a jury of residents of that county. However, since it was not assigned to a judicial district, it had no judiciary or prosecutors. Additionally, if a felony or serious misdemeanor was committed in Bullfrog County, it would have been theoretically impossible to empanel a jury,  a (perhaps) perfect crime. For these and other reasons, Nye County sued, claiming the law was unconstitutional. In late October 1987, Nevada Attorney General Brian McKay announced that the state would not defend the law in court, since in his view it was likely unconstitutional. 
On February 11, 1988, retired Nevada Supreme Court justice David Zenoff conducted a special hearing and found Bullfrog County's creation to be unconstitutional. Zenoff found that since Bullfrog County had no residents, it did not have a representative government. He also ruled the provision of the law giving Bryan the power to appoint the commissioners and sheriff ran counter to the democratic process. In compliance, the state legislature abolished Bullfrog County in 1989, and the territory was retroceded to Nye County. 
- Hillinger, Charles (September 2, 1987). "Bullfrog, Nevada: Empty County to Croak Unless It Goes to Waste". Los Angeles Times.
- Legislative History, AB 756 (1987) (PDF) (Report). Nevada Legislature. Retrieved 2018-05-07.
- Knudson, Thomas J. (August 30, 1987). "Bullfrog County, Nev., (Pop. 0) Fights Growth". The New York Times.
- "RE: Swiss experts back deep storage for nuclear waste". Archived from the original on October 25, 2006. Retrieved August 16, 2010.
- "Nevada Governor Gives Up on Bullfrog County". Los Angeles Times. Associated Press. November 1, 1987. Retrieved November 10, 2012.
- Titus, A. Costandina (1990). "Bullfrog County: A Nevada Response to Federal Nuclear-Waste Disposal Policy". Publius: The Journal of Federalism. 20 (1): 123–135. doi: 10.1093/oxfordjournals.pubjof.a037849. Retrieved 2018-05-07.