New Gretna is an unincorporated community and census-designated place located within Bass River Township in Burlington County, in the U.S. state of New Jersey. The area is served as United States Postal Service ZIP Code 08224.As of the 2010 United States Census, the population for ZIP Code Tabulation Area 08224 was 573. The population for the ZCTA as of the 2000 United States Census was 543.