The county is named for Oneida Lake, New York, the area from which most of the early settlers had emigrated.

[4] The county seat was moved to Malad City in 1866 because of its population growth and location on the freight road and stagecoach line between Corinne, Utah, and the mines in Butte, Montana.

Its initial size was 32,708 mi2 making it the third largest of the 17 counties created by the first legislature of Idaho Territory in 1863 and early 1864.

Minor changes to boundaries occurred in 1917 and 1927 that gave Oneida County its present land area.

Early loss of territory had no impact on population growth of the county as some areas lost had almost no population or were offset by heavy migration of Mormons occurring along Idaho's southern border.

However, the county's actual population was severely undercounted as a result of its lack of a surveyed southern boundary.

Oneida County did retain developing population centers at Malad City, American Falls, and Preston.

The loss in territory again caused a population decline while Malad City and even outlying areas experienced growth through the 1920 Census.

[9] Oxford Peak is the highest point in the county at 9,285 ft (2,830 m) above sea level.

Alternating valleys and ridges of mountains or hills typify the topography, with grassland and sagebrush covering most areas.

22.50% of all households were made up of individuals, and 11.90% had someone living alone who was 65 years of age or older.

As of the 2010 United States Census, there were 4,286 people, 1,545 households, and 1,161 families living in the county.

[17] In terms of ancestry, 38.3% were English, 15.1% were Welsh, 12.8% were "American", 10.7% were German, 5.8% were Swedish, and 5.1% were Danish.