Delaware counties by area

Understanding Delaware’s county areas

The land-area range runs from New Castle County at 426.3 mi² to Sussex County at 936.2 mi². The largest has 2.2 times the land area of the smallest and accounts for 48% of the combined county land in Delaware. Compare with every state’s largest county.

The median county-equivalent land area is 586.1 mi², below the national median of 604.5 mi². The median describes the middle of the county size distribution; it does not describe how people or development are distributed. A state with a few very large counties can have a much smaller median than its largest entry suggests.

Where water changes the picture

Sussex County has the most assigned water area, at 260.2 mi². Kent County has the highest water share, with water making up 26.6% of its total area. Water area and water percentage answer different questions: the first measures an amount, while the second measures the mix of land and water.

Across all 3 entries, water accounts for 21.7% of the combined total area. This is calculated from the summed land and water measurements, rather than averaging county percentages, which would give each small and large county equal weight.

Where people live

An estimated 1,059,952 people lived in Delaware on July 1, 2025 (+7.1% since 2020), or 0.3% of the national total in this dataset. New Castle County is the most populous county equivalent, with 588,026 residents — 55.5% of the state. The largest by land, Sussex County, has 277,140.

Across the state there are 544 people per square mile of land. County densities range from 1,379 in New Castle County to 296 in Sussex County; the median county equivalent has 332. Switch the map above to density to see where the state’s population concentrates.

Compare the largest and smallest county equivalents in Delaware to see land, water, and total area on the same scale.

These calculations use the 2026 Census county records listed below. County-equivalent boundaries vary between states; area alone does not measure population, density, or usable land. See coverage and calculation rules.