[2] Originally designated as part of the Cherokee Outlet, it was named County L in Oklahoma Territory at the time of its opening to non-Indian settlement.

Settlers named the county after President Ulysses S. Grant[3] in a general election held November 6, 1894.

In 1897, the Gulf Railroad (later the Atchison, Topeka and Santa Fe Railway, AT&SF) linked Manchester, Wakita, Medford, and Deer Creek.

At the start of the 20th century, the Blackwell, Enid and Southwestern Railroad (later the St. Louis and San Francisco Railway) passed through Lamont.

[4] Bethel was the site of a post office in Grant County that existed from March 12, 1895, until November 2, 1895.

[5] Florence was the site of a post office in Grant Co. that existed prior to 1908 but ceased to exist circa 1920, after the post office closed, per information acquired in researching an ancestor, Isaac Arnold, who was postmaster in Florence from August 1908 to 1920.

[7] Most of the county is drained by the Salt Fork of the Arkansas River and its tributaries (Pond, Deer, Osage, and Crooked creeks).

Less than 1 percent of the population self-identified as Black or African American, Asian, or Pacific Islander.

At statehood the principal crops included wheat, corn, oats, alfalfa, and forage sorghum with estimated value of $3.5 million.

[4] Oil and gas were discovered In the early 1920s in the eastern part of the county near the Blackwell Field.