Phelps County is a county located in the central portion of the U.S. state of Missouri. As of the 2010 census, the population was 45,156. The largest city and county seat is Rolla. The county was officially organized on November 13, 1857, and was named after U.S. Representative and Governor of Missouri John Smith Phelps.
According to the U.S. Census Bureau, the county has a total area of 674 square miles (1,750 km), of which 672 square miles (1,740 km) is land and 2.5 square miles (6.5 km) (0.4%) is water.
As of the census of 2000, there were 39,825 people, 15,683 households, and 10,240 families residing in the county. The population density was 59 people per square mile (23/km²). There were 17,501 housing units at an average density of 26 per square mile (10/km²). The racial makeup of the county was 93.24% White, 1.50% Black or African American, 0.59% Native American, 2.35% Asian, 0.06% Pacific Islander, 0.47% from other races, and 1.79% from two or more races. Approximately 1.22% of the population were Hispanic or Latino of any race.
There were 15,683 households out of which 30.30% had children under the age of 18 living with them, 52.70% were married couples living together, 9.50% had a female householder with no husband present, and 34.70% were non-families. 28.60% of all households were made up of individuals and 10.70% had someone living alone who was 65 years of age or older. The average household size was 2.38 and the average family size was 2.92.
In the county, the population was spread out with 23.70% under the age of 18, 14.50% from 18 to 24, 26.10% from 25 to 44, 21.80% from 45 to 64, and 13.90% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 103.20 males. For every 100 females age 18 and over, there were 102.90 males.
The median income for a household in the county was $37,243, and the median income for a family was $49,343. Males had a median income of $29,428 versus $19,893 for females. The per capita income for the county was $20,275. About 11.30% of families and 16.40% of the population were below the poverty line, including 19.00% of those under age 18 and 13.00% of those age 65 or over.
According to the Association of Religion Data Archives County Membership Report (2000), Phelps County is a part of the Bible Belt with evangelical Protestantism being the majority religion. The most predominant denominations among residents in Phelps County who adhere to a religion are Southern Baptists (38.24%), Roman Catholics (11.43%), and Christian Churches & Churches of Christ (10.75%).