Delaware Counties by Population (2025)

There are 3 counties in Delaware.

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 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: Growing the fastest with a population increase of 15.87% since the 2010 Census.
• Kent County: Population has grown 9.57% since the 2010 Census.
• New Castle County: Population has grown 3.82% since the 2010 Census.