According to the 2000 U.S. Census, the county has a total area of 677.80 square miles (1,755.5 km2), of which 674.97 square miles (1,748.2 km2) (or 99.58%) is land and 2.82 square miles (7.3 km2) (or 0.42%) is water.
There were 97,859 households out of which 28.30% had children under the age of 18 living with them, 50.00% were married couples living together, 9.80% had a female householder with no husband present, and 36.80% were non-families. 29.10% of all households were made up of individuals and 9.70% had someone living alone who was 65 years of age or older. The average household size was 2.34 and the average family size was 2.89.
In the county the population was spread out with 22.30% under the age of 18, 13.80% from 18 to 24, 28.60% from 25 to 44, 21.80% from 45 to 64, and 13.60% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 94.40 males. For every 100 females age 18 and over, there were 91.20 males.
The median income for a household in the county was $44,185, and the median income for a family was $56,047. Males had a median income of $30,672 versus $21,987 for females. The per capita income for the county was $25,770. About 7.60% of families and 12.10% of the population were below the poverty line, including 13.60% of those under age 18 and 7.50% of those age 65 or over.
There are 190,417 registered voters in Greene County.
Like most counties situated in Southwest Missouri, Greene County is a Republican stronghold in presidential elections. Although the county contains the urban Springfield and Missouri State University, the county is located in the heart of the Bible Belt where voters tend to be very socially conservative and therefore more amendable to voting Republican. George W. Bush carried Greene County in 2000 and 2004 by almost two-to-one margins, and like many other counties throughout the Bible Belt in Southwest Missouri, Greene County favored John McCain over Barack Obama in 2008. The last Democratic presidential nominee to win Greene County was Lyndon B. Johnson in 1964.
Like most areas throughout the Bible Belt in Southwest Missouri, voters in Greene County traditionally adhere to socially and culturally conservative principles which tend to strongly influence their Republican leanings. In 2004, Missourians voted on a constitutional amendment to define marriage as the union between a man and a woman—it overwhelmingly passed Greene County with 72.04 percent of the vote. The initiative passed the state with 71 percent of support from voters as Missouri became the first state to ban same-sex marriage. In 2006, Missourians voted on a constitutional amendment to fund and legalize embryonic stem cell research in the state—it narrowly failed in Greene County with 51.62 percent voting against the measure. The initiative narrowly passed the state with 51 percent of support from voters as Missouri became one of the first states in the nation to approve embryonic stem cell research. Despite Greene County’s longstanding tradition of supporting socially conservative platforms, voters in the county have a penchant for advancing populist causes like increasing the minimum wage. In 2006, Missourians voted on a proposition (Proposition B) to increase the minimum wage in the state to $6.50 an hour—it passed Greene County with 74.41 percent of the vote. The proposition strongly passed every single county in Missouri with 78.99 percent voting in favor as the minimum wage was increased to $6.50 an hour in the state. During the same election, voters in five other states also strongly approved increases in the minimum wage.
Voters in Greene County from both political parties supported candidates who finished in second place in the state at large and nationally.
Although a conservative/Republican stronghold, former U.S. SenatorHillary Rodham Clinton (D-New York) still received more votes, a total of 18,322, than any candidate from either party in Greene County during the 2008 presidential primary.