[2] The county was founded in 1870 and is named for Congressman John Preston Martin.

In 1964, President Lyndon Johnson visited Inez, where he announced the launch of the War on Poverty.

[6] The county's eastern border is formed by the Tug Fork of the Big Sandy River.

As of the census[13] of 2000, there were 12,578 people, 4,776 households, and 3,620 families residing in the county.

21.80% of all households were made up of individuals, and 8.30% had someone living alone who was 65 years of age or older.

The Federal Bureau of Prisons U.S. Penitentiary, Big Sandy is located in unincorporated Martin County, near Inez.