Population of Counties in Delaware (2020)

Of Delaware’s three counties, the most populous is New Castle County. New Castle County has a population of 559,335 people, comprising 57.83% of the state’s total population. New Castle County has a population density of 1,312.11 persons per square mile.

Delaware Counties with the Fewest Residents

The least populated of Delaware’s three counties is Kent County, which has a population of 178,550 people. This is about 18.46% of Delaware’s total population.

Sussex County is Delaware’s second-least populated county and second-most populated county with 229,286 people. Sussex County makes up about 23.71% of the state’s total population.

Delaware Counties with Rapid Growth

Unlike many counties in other states, all three of Delaware’s counties are experiencing considerable population growth. Sussex County is growing the fastest of the three with its population increasing 15.87% since the 2010 Census. This is followed by Kent County and then New Castle County, which have grown 9.57% and 3.82% respectively since the 2010 Census.