23.60% of all households were made up of individuals and 10.40% had someone living alone who was 65 years of age or older.The average household size was 2.64 and the average family size was 3.13. For every 100 females age 18 and over, there were 93.70 males.In 1879 it was partitioned away from Owyhee County to form part of Cassia County.The county is named for a split waterfall on the Snake River of the same name. Even after Idaho became a state in 1890, the Twin Falls area was very sparsely populated and without significant settlements.
Males had a median income of ,777 versus ,257 for females. About 10.6% of families and 13.0% of the population were below the poverty line, including 16.9% of those under age 18 and 10.7% of those age 65 or over.
That changed after the city of Twin Falls was founded in 1904 and Milner Dam was completed in 1905.
Most of the county's other towns were established during this period as well.
The population density was 33 people per square mile (13/km²).
There were 25,595 housing units at an average density of 13 per square mile (5/km²).