Boyd county was formed in 1860. It is located in the Eastern Coal Field region of the state. The elevation in the county ranges from 515 to 1140 feet above sea level. In 2010 the county population was 49,542 in a land area of 159.86 square miles, an average of 309.9 people per square mile.

The county seat is Catlettsburg.

The largest city in the county is Ashland.