Divide County's earliest known inhabitants included the Assiniboine, who crossed the area between seasonal homes and left petroglyphs at Writing Rock in the county's far west. Before settlement, ranchers near the Missouri River used the land for grazing and drove cattle into Canada near present-day Ambrose around 1867. Settlers arrived around 1902, drawn by some of the last unclaimed land available under the United States Homestead Acts. Divide County was created in 1910 after an election dividing Williams County, and Crosby, founded in 1904 at the end of a Great Northern Railway branch line and also served by the Soo Line Railroad, became first the temporary and then the permanent county seat; it was named for businessman S.A. Crosby, who helped establish it. Small grain farming and ranching remained the county's primary economic base, while coal surface mining and a United States Air Force radar station contributed during the 1900s and oil and gas exploration played major roles in the 2000s; the county now has about 2,500 residents. The community also honors North Dakota veterans including Crosby native Corporal David D. Elsbernd, a Gold Star casualty killed in Vietnam in 1969 by a rocket grenade and honored on the Vietnam Memorial in Washington, D.C.; Henry Gurke, who on November 9, 1943, sacrificed himself by smothering a grenade in a foxhole to save a fellow Marine; Woodrow W. Keeble, whose leadership and assault on three fortified enemy machine-gun positions earned him a Distinguished Service Cross and later the Medal of Honor; and Willis W. Bradley, awarded the Medal of Honor for stopping burning materials near powder aboard the U.S.S. Pittsburgh after an accidental ammunition explosion.