"Yonkers" is entirely unrelated to "Yankee".

From the Library of Congress:

"Yonkers, N.Y.        This name is believed to derive from the title of an early Dutch settler, Jonkheer Adriaen Van der Donck, who had an estate in the area. Van der Donck wrote one of the first accounts of the New Netherland settlement."

Or here:

"We learn that the name for the area of Yonkers originated from Van der Donck himself, who resided on a huge tract of land north of Manhattan and whose title Jonker, or young squire, would forever be fused with the territory."

(From a review of "The Island at the Center of the World: The Epic Story of Dutch Manhattan, the Forgotten Colony That Shaped America"
By Russell Shorto, Doubleday -- I'd heard an interview with him recently.)

~ Becky in Tucson