The board voted 15-3 on Monday night to turn down Minard Run Oil Company's request for a permit to drill near Downs. The town is about 15 miles southeast of Bloomington.
Board member George Gordon noted some evidence was presented that the proposed drilling location wouldn't be close enough to the Mahomet aquifer to pollute it. But he said that information didn't include underground tributaries that might feed into the water source.
The aquifer sits deep under much of central Illinois and is a water source for many towns.
But board member Paul Segobiano said fears about the aquifer were unfounded.