As of March 23, 2011, there were a total of 20,722 registered voters in Plainfield, of which 12,078 (58.3% vs. 41.8% countywide) were registered as Democratic Party (United States), 947 (4.6% vs. 15.3%) were registered as Republican Party (United States) and 7,693 (37.1% vs. 42.9%) were registered as Unaffiliated (New Jersey). There were 4 voters registered to other parties. Among the citys 2010 Census population, 41.6% (vs. 53.3% in Union County) were registered to vote, including 56.1% of those ages 18 and over (vs. 70.6% countywide).. How many more voters were registered as Democratic Party, by percent,  in Plainfield compared to Union County?