The genetic variability of the major essential oil constituents in a germplasm collection of dill (Anethum graveolens L.) from the National Plant Germplasm System was characterized. The oil content in the dill herb ranged from 0.10% to 0.30% (v/fresh weight), and in the dill seed from 1.75% to 4.0% (v/dry weight). The three major constituents in the dill herb oil were α-phellandrene, β-phellandrene, and 3,9-oxy-p-menth-1-ene (dill ether) comprising 90% to 97% of the total oil constituents. Of these three constituents, α-phellandrene comprised 51.1% to 64.7% of the total oil. The major constituents in dill seed oil were carvone and dihydrocarvone comprising 68% to 83% of the total oil constituents. The other major constituent was limonene, which ranged from 14.18% to 21.43%. Carvone was not detected in the herb oil; and dill ether could not be detected in the seed oil.