The Delaware state seal was first adopted in 1777. The state coat of arms is surrounded by the inscription "Great Seal of the State of Delaware," with three dates below:

1704 - year of the first Delaware General Assembly.
1776 - year independence was declared from Great Britain.
1787 - year Delaware ratified the United States Constitution
            (becoming the first state).

The state coat of arms (also displayed on the state flag) was first adopted in 1777 and contains many symbols of Delaware:

Ship - a symbol of Delaware's ship building industry and extensive coastal commerce.

Farmer - represents the central role of farming to the state of Delaware.

Militiaman - recognizes the crucial role of the citizen-soldier to the maintenance of American liberties.

Wheat Sheaf - a symbol of the agricultural vitality of Delaware.

Maize (Indian Corn) - symbolizes the agricultural basis of Delaware's economy.

Water - represents the Delaware River, the state's main artery of commerce and transportation.

Ox - signifies the importance of animal husbandry to Delaware's state economy.

Motto - "Liberty and Independence" was approved in 1847.

Source:

Delaware Facts and Symbols State Seal: Delaware.gov

Links:

State Seals - 50 States List
National Seal