[2] The Dakota Territory legislature created Ransom County on January 4, 1873.

Ransom County has retained its present configuration since that time.

The county terrain consists of rolling hills, dotted with lakes and ponds in its western part.

[5] The terrain slopes to the east and south; its highest point is on the north boundary line near its northwestern corner, at 1,421 ft (433 m) ASL.

The racial makeup of the county was 97.8% white, 0.4% Asian, 0.4% American Indian, 0.3% black or African American, 0.1% Pacific islander, 0.1% from other races, and 0.9% from two or more races.

In terms of ancestry, 54.2% were German, 36.6% were Norwegian, 9.0% were Irish, 6.9% were Swedish, 5.1% were English, and 1.6% were American.

The county broke its bellwether streak in 1988 and 2020, voting for the Democratic nominee Michael Dukakis in 1988 and Republican nominee Donald Trump in 2020, who both would lose the general election.

In the 2018 election for U.S. Senate, it gave Heidi Heitkamp her 4th-highest total (60.6%), behind only Sioux, Rolette, and Benson counties.