John M. Barry, Distinguished Visiting Scholar, the Center for Bioenvironmental Research of Tulane and Xavier Universities, New Orleans, Louisiana, concluded that Haskell County was the location of the first outbreak of the Spanish flu of 1918, which killed between 21 and 100 million people. The same point is made in his critically acclaimed book The Great Influenza; The Story of the Deadliest Pandemic in History. Dr. Loring Miner, a tough and intelligent Haskell County doctor, warned the editors of Public Health Reports of the U.S. Public Health Service about the new and more deadly variant of the virus. It produced the common influenza symptoms with a new intensity: "violent headache and body aches, high fever, non-productive cough. . . . This was violent, rapid in its progress through the body, and sometimes lethal. This influenza killed. Soon dozens of patients—the strongest, the healthiest, the most robust people in the county—were being struck down as suddenly as if they had been shot."  Barry writes that "In the first six months of 1918, Miner's warning of 'influenza of a severe type' was the only reference in that journal to influenza anywhere in the world.
The railroad and the development of oil and gas fields in the 1930s, and the locating of many deep wells for irrigation significantly improved the economy of the area helping overcome the "dust bowl" of that period. Haskell County was one of the hardest hit counties in the Midwest during the drought of 1930-1937.
The first rodeo and fair was held in Sublette in 1916 and the fair continues at the same location. The first school district was founded in Santa Fe in 1887. Amanda I. Watkins, who owned a considerable amount of land in the county, was named "World Wheat Queen" in 1926.
Although the Kansas Constitution was amended in 1986 to allow the sale of alcoholic liquor by the individual drink with the approval of voters, Haskell County has remained a prohibition, or "dry", county.
There were 1,481 households out of which 43.60% had children under the age of 18 living with them, 69.40% were married couples living together, 5.90% had a female householder with no husband present, and 22.10% were non-families. 20.10% of all households were made up of individuals and 9.20% had someone living alone who was 65 years of age or older. The average household size was 2.88 and the average family size was 3.35.
In the county the population was spread out with 32.90% under the age of 18, 9.10% from 18 to 24, 27.80% from 25 to 44, 19.50% from 45 to 64, and 10.60% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 103.30 males. For every 100 females age 18 and over, there were 98.30 males.
The median income for a household in the county was $38,634, and the median income for a family was $43,354. Males had a median income of $31,296 versus $22,857 for females. The per capita income for the county was $17,349. About 8.00% of families and 11.60% of the population were below the poverty line, including 15.40% of those under age 18 and 9.40% of those age 65 or over.
Haskell County is divided into three townships. None of the cities within the county are considered governmentally independent, and all figures for the townships include those of the cities. In the following table, the population center is the largest city (or cities) included in that township's population total, if it is of a significant size.