The most predominant denominations among residents in Grundy County who adhere to a religion are Southern Baptists (49.86%), United Methodists (13.51%), and Disciples of Christ (6.95%).

Source[13] The Republican Party predominantly controls politics at the local level in Grundy County.

Grundy 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).

Like most rural areas throughout northern Missouri, voters in Grundy County generally adhere to socially and culturally conservative principles which tend to influence their Republican leanings.

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

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

Businessman Donald Trump (R-New York) narrowly won the state overall, but received majority support in Grundy County.

On the Democratic side, former Secretary of State Hillary Clinton (D-New York) won statewide by a slim margin, but Senator Bernie Sanders (I-Vermont) carried Grundy 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 Grundy 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.