Welcome to the bluffs of the Missouri River Valley. Dixon County is home to 6,000 people (2010) and the county seat is Ponca.
In addition to the city of Ponca, Dixon County is home to the communities of Maskell, Newcastle, Martinsburg, Waterbury, Allen, Dixon, Concord, and a portion of Wakefield. I could not find any reference to the person after which the county was named.
Settling the townsite of Ponca: (from the Virtual Nebraska website)
Adam Smith, his wife, and nine other settlers crossed the Missouri into Nebraska in 1856 and camped south of the Aowa Creek, since to the north was “Indian territory.