As of the census of 2000, there were 16,800 people, 6,847 households, and 4,697 families residing in the county.

There were 7,754 housing units at an average density of 32 per square mile (12/km2).

27.60% of all households were made up of individuals, and 12.80% had someone living alone who was 65 years of age or older.

Mason County was at the time of the Civil War the easternmost of the strongly secessionist Bluegrass bloc.

Mason County's secessionist sentiment meant that it voted Democratic consistently up until the 1950s, with the exception of the 1928 election when strong local anti-Catholic sentiment against Al Smith allowed Herbert Hoover to carry the county.

Since 1996 the county has shifted more strongly Republican in US presidential elections.