According to the US Census Bureau, the most diverse cities in New Jersey are:
These cities have large and diverse populations, with residents from a variety of racial and ethnic backgrounds. The rankings may be different if you were to consider other factors, such as the size of the population or the number of languages spoken.
Note, that the Census Bureau collects data on the population, demographics, and housing characteristics of cities and other geographic areas throughout the United States. This data can be used to identify cities with large and diverse populations.
The Census Bureau conducts a census every ten years, and it also collects data through other ongoing surveys and programs, such as the American Community Survey (ACS) and the Population Estimates Program (PEP). These data sources provide a wealth of information on the population, demographics, and housing characteristics of cities and other geographic areas.