[2] The county was officially organized on January 29, 1841, and was named in honor of George F. "Peg-Leg" Shannon, a member of the Lewis and Clark Expedition.

Among the major first ancestries reported in Shannon County were 38.3% American, 13.4% Irish, 11.8% German, and 9.7% English.

The Republican Party predominantly controls politics at the local level in Shannon County.

Smith won a special election on Tuesday, June 4, 2013, to finish out the remaining term of U.S. Representative Jo Ann Emerson (R-Cape Girardeau).

Emerson announced her resignation a month after being reelected with over 70 percent of the vote in the district.

Like most rural areas throughout Southeast Missouri, voters in Shannon County generally adhere to socially and culturally conservative principles.

The proposition strongly passed every single county in Missouri with 75.94 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.

In the 2008 presidential primary, voters in Shannon County from both political parties supported candidates who finished in second place in the state at large and nationally.

Senator Hillary Clinton (D-New York) received more votes, a total of 914, than any candidate from either party in Shannon County during the 2008 presidential primary.