The 1966 Idaho gubernatorial election was held on November 8. Republican nominee Don Samuelson defeated Democratic nominee Cecil Andrus with 41.4% of the vote in a four-way race (two independents).
In early August, three-term incumbent Robert E. Smylie, the dean of American governors, was soundly defeated in the Republican primary by Samuelson. Andrus was a close runner-up in the Democratic primary to Charles Herndon, who was killed in a plane crash six weeks later in September.
This was the sixth consecutive Republican victory for governor, but Democrats won the next six, with four by Andrus. The next gubernatorial election in 1970 was a rematch, with different results.
Primary elections.
Primary elections were held on August 2, 1966.
Democratic primary.
Results.
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
Republican primary.
Results.
! scope="col" colspan="2" style="width: 15em" |Party
! scope="col" style="width: 17em" |Candidate
! scope="col" style="width: 5em" |Votes
! scope="col" style="width: 3.5em" |%
! colspan="3" style="text-align:right;" | Total votes
General election.
Candidates.
Major party candidates
Other candidates
Results.
! scope="col" colspan="2" style="width: 130px"|Party
! scope="col" style="width: 17em"|Candidate
! scope="col" style="width: 5em"|Votes
! scope="col" style="width: 3.5em"|%
! scope="col" style="width: 3.5em"| ;templatestyles src="Template:Tooltip/styles.css" / ;±%
! colspan="3" style="text-align: right; margin-right: 0.5em" | Majority
! colspan="3" style="text-align: right; margin-right: 0.5em" scope=row | Turnout
! style="text-align:right;" | Swing
References.
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