According to the U.S. Census Bureau, the county has a total area of 1,001 km² (386 mi²). 988 km² (381 mi²) of it is land and 13 km² (5 mi²) of it (1.28%) is water.
No federal roads run through Perry County, except for Interstate 64, which runs extremely close to its northern boundaries. Indiana State Highway 66, designated as the Ohio River Scenic Byway for most of its course in the county, is the most heavily traveled road by residents and visitors alike, adjacent to the three most populated towns in the county as well as most major tourist destinations. Indiana Route 37 is used by most in the county as a way out, directly going to Bloomington and Indianapolis. Other state roads in the county include IN-62, which closely parallels I-64, IN-145, which cuts through the western parts of the county, IN-166, which is little more than a road to and from the hamlet of Tobinsport, IN-237, which connects Cannelton directly to IN-37 (also the site of a bridge on the Ohio River), and a short run of IN-545 near Troy.
Perry County was formed in 1814. It was named for Commodore Oliver Hazard Perry who defeated the British squadron in the decisive Battle of Lake Erie in 1813.
align=center 2000 18,899 1990 19,107 1980 19,346 1970 19,075 1960 17,232 1950 17,367 1940 17,770 1930 16,625 1920 16,692 1910 18,078 1900 18,778 |}As of the census2 of 2000, there were 18,899 people, 7,270 households, and 5,074 families residing in the county. The population density was 19/km² (50/mi²). There were 8,223 housing units at an average density of 8/km² (22/mi²). The racial makeup of the county was 97.61% White, 1.45% Black or African American, 0.17% Native American, 0.12% Asian, 0.02% Pacific Islander, 0.13% from other races, and 0.50% from two or more races. 0.70% of the population were Hispanic or Latino of any race.
There were 7,270 households out of which 30.60% had children under the age of 18 living with them, 56.70% were married couples living together, 9.00% had a female householder with no husband present, and 30.20% were non-families. 26.70% of all households were made up of individuals and 12.70% had someone living alone who was 65 years of age or older. The average household size was 2.45 and the average family size was 2.96.
In the county the population was spread out with 22.90% under the age of 18, 9.80% from 18 to 24, 29.20% from 25 to 44, 23.30% from 45 to 64, and 14.90% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 107.00 males. For every 100 females age 18 and over, there were 107.70 males.
The median income for a household in the county was $36,246, and the median income for a family was $43,743. Males had a median income of $31,554 versus $22,123 for females. The per capita income for the county was $16,673. About 7.10% of families and 9.40% of the population were below the poverty line, including 12.30% of those under age 18 and 8.90% of those age 65 or over.
