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.

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.

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.