The vehicle driven by Todd M. Delong, Jr., 19, of Lewisburg appeared to hit a bump in the road, overturn and roll several times, the Darke County Sheriff's Office said.
The 2004 Kia came to rest in a field on its side, scattering debris in all directions and ejecting Kaitlyn Moses, 17, of Eldorado, who was pronounced dead at the scene.
Delong and Derek Baker, 18, of Arcanum, were wearing seat belts and were not ejected.
Investigators are unsure if the third passenger, Taylor V. Landis, 19, of Eldorado, was also ejected.
Delong and Landis were flown from the scene aboard CareFlight, and Arcanum Rescue removed Baker to Miami Valley Hospital in Dayton.
Delong and Baker were treated and released, and Landis is in fair condition, a Miami Valley Hospital spokesperson said.
Darke County deputies are handling the investigation and suspect speed and alcohol were factors in the crash.
Crash re-constructionists from Darke County and neighboring Miami County were still on the scene as of 5 a.m. attempting to determine what caused the crash, along with trying to estimate how fast the vehicle was traveling at the time.