The most predominant denominations among residents in Buchanan County who adhere to a religion are Southern Baptists (24.96%), Roman Catholics (20.35%), and nondenominational evangelical groups (15.95%).

Buchanan County is split between three legislative districts in the Missouri House of Representatives, all of which are held by Republicans.

Buchanan County, along with the rest of the state of Missouri, is represented in the U.S. Senate by Josh Hawley (R-Columbia) and Roy Blunt (R-Strafford).

On the Democratic side, former Vice President Joe Biden (D-Delaware) both won statewide and carried Buchanan County by a wide margin.

Incumbent President Donald Trump (R-Florida) faced a primary challenge from former Massachusetts Governor Bill Weld, but won both Buchanan County and statewide by overwhelming margins.

Businessman Donald Trump (R-New York) narrowly won the state overall and carried a plurality in Buchanan County.

On the Democratic side, former Secretary of State Hillary Clinton (D-New York) narrowly won statewide, but Senator Bernie Sanders (I-Vermont) carried Buchanan County.

Senator Rick Santorum (R-Pennsylvania), who finished first in the state at large, but eventually lost the nomination to former Governor Mitt Romney (R-Massachusetts).

In 2008, the Missouri Republican Presidential Primary was closely contested, with Senator John McCain (R-Arizona) prevailing and eventually winning the nomination.

Then-Senator Hillary Clinton (D-New York) received more votes than any candidate from either party in Buchanan County during the 2008 presidential primary.

Despite initial reports that Clinton had won Missouri, Barack Obama (D-Illinois), also a Senator at the time, narrowly defeated her statewide and later became that year's Democratic nominee, going on to win the presidency.