As of the census of 2000, there were 18,812 people, 7,402 households, and 5,477 families residing in the county.  The population density was 55 people per square mile (21/km²).  There were 10,319 housing units at an average density of 30 per square mile (12/km²).  The racial makeup of the county was 51.45% Race (United States Census), 41.90% Race (United States Census) or Race (United States Census), 0.20% Race (United States Census), 0.66% Race (United States Census), 0.04% Race (United States Census), 0.82% from Race (United States Census), and 0.92% from two or more races.  2.16% of the population were Race (United States Census) or Race (United States Census) of any race.. How many more housing units are there than families?