The county was created by the Utah Territory legislature on January 13, 1854, with its description containing a portion of the future state of Wyoming.

It was not organized then but was attached to Great Salt Lake County for administrative and judicial purposes.

Its final alteration occurred on January 7, 1918, when Daggett's creation took a portion of its eastern territory.

Summit County lies on the upper east side of Utah.

There were 15,688 households in Summit County with an average size of 2.70 of which 11,419 (72.8%) were families and 4,269 (27.2%) were non-families.

[citation needed] Summit County was a Republican stronghold in the decades following World War II.

Beginning in the 1990s, it became more competitive due to the influence of Democratic-leaning Park City, with Democrats sometimes winning a plurality or majority of the countywide vote.

George W. Bush carried the county in 2000 and 2004, but his performance there was worst in the state.

[16] In the 2012 presidential election, Republican Mitt Romney defeated Obama in the county, 50% to 46%.

In June 2010, Summit County became the sixth local government of Utah to prohibit discrimination in employment or housing based on a person's sexual orientation or gender identity.