Jefferson County is part of the St. Louis Metropolitan Statistical Area and encompasses many of the city's southern suburbs.

[15] Jefferson College - Hillsboro: A public, two-year community college Historically, the Democratic Party has controlled politics at the local level; starting in 2010 the Republican Party has flipped the county with 66% of the population voting Republican in 2020.

Jefferson County is divided into seven legislative districts in the Missouri House of Representatives; all of which are held by Republicans.

Bill Clinton, however, did manage to carry Jefferson County by double digits both times in 1992 and 1996.

However, in 2012 the county, in line with the state as a whole, began to swing hard to the right with Mitt Romney carrying it with 55% of the vote.

In 2016 Donald Trump won the county with 65% of the vote, the largest margin of any candidate since Lyndon Johnson in 1964.

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.

Libertarian-leaning U.S. Representative Ron Paul (R-Texas) finished a distant fourth place with 3.94% of the vote in Jefferson County.

McCain received all of Missouri's 58 delegates as the Republican Party utilizes the winner-takes-all system.

Senator John Edwards (D-North Carolina) still received 2.74% of the vote in Jefferson County.

Clinton had a large initial lead in Missouri at the beginning of the evening as the rural precincts began to report, leading several news organizations to call the state for her; however, Obama rallied from behind as the heavily African American precincts from St. Louis began to report and eventually put him over the top.

Hillary Rodham Clinton received more votes, a total of 19,075, than any candidate from either party in Jefferson County during the 2008 Missouri Presidential Primaries.

According to a 2012 census study by the University of Wisconsin Population Health Institute and the Robert Wood Johnson Foundation, Jefferson County led the Saint Louis metropolitan area in the number of adults who smoke, roughly 30% of all adult residents of Jefferson County smoked or used tobacco in some form, compared to the 19% national average and the 24% Missouri state average.

[29][30] Jefferson County and the state of Missouri led the nation in methamphetamine production, peaking in the mid-2000s.