It was formed in 1808 from Clark and Madison counties. Estill county was a source of Breathitt (1839), Owsley (1843), Powell (1852), Jackson (1858), and Lee (1870) counties. The county seat is Irvine.
In 2010 the county population was 14,672 in a land area of 253.08 square miles, an average of 58.0 people per square mile.
The equine population was 1,000 in the 2012 Kentucky Equine Survey.
Estill county was named for Captain James Estill, an early settler in what is now Madison county.
Much of Estill county lies within the Daniel Boone National Forest.