I was just on an insurance website that listed DuVal as the county we're in. Some people go by DuWhatever, while others use DuSomething. Still others are du Frenchplace. So, I wonder what the deal is with Duval.
Duval County is named after William Pope Duval, who was the first governor of Florida. He was an appointed governor, so it's not like the people of the state voted for him, but he did rule over Florida for twelve years. Duval himself went by Duval, as can be seen in his signature:
Of course, Duval, regardless of how William spelled it, would have been du Val at one point. Just like duPont (as in Jessie Ball duPont), used to be du Pont, though I am sure some people around Duval County call it Dupont.
One additional tidbit about William Duval's name is that he had three sons, with two of them going by Duval and one going by DuVal. Burr and John were Duval, and Duval County, Texas is named after Burr. Thomas, the obvious attention-seeking middle child, went by DuVal.
To recap, the person specifically for whom Duval County was named was named Duval, not du Val, duVal, or DuVal. So, unlike St. Johns, which people from Florida changed because...lazy, Duval County is spelled correctly. With ONE u, not three.