The half which became Arthur County had been in the process of settlement by 1884, by ranchers seeking open grazing land.

The placement of a post office at Lena in 1894 and the passage of the homesteading act in 1904 (which allowed claims of 640 acres compared to the previous 160 acres in this area) further influenced the county's founding and expedited the new county's establishment processes.

[4] Principal postal service moved from Lena to the village of Arthur in 1914, which also held the county's public schools, general store, bank and co-op, principal churches, newspaper and other businesses and services, all aimed at continuing and facilitating the county's rural lifestyle.

The 1920 United States Census counted 1,412 residents in Arthur County, which was then and has remained entirely rural, essentially ranching.

Although the village of Arthur underwent electrification in the 1920s, most of the county did not see power or telephone services until 1950–1951.

The racial makeup of the county was 96.1% White, 0.9% Native American, 0.2% Asian, 0.00% Pacific Islander, 2.8% from two or more races.

As of the 2000 United States Census,[11] of 2000, there were 444 people, 185 households, and 138 families residing in the county.

21.60% of all households were made up of individuals, and 10.80% had someone living alone who was 65 years of age or older.