Roosevelt narrowly carried New Jersey with 51.55% of the vote to Dewey's 47.93%, a margin of 3.62%. 
Reflecting the closeness of the statewide result, Roosevelt and Willkie virtually split the state's 21 counties: Roosevelt won 11 counties to Willkie's 10. Roosevelt edged out Willkie statewide with decisive victories in some of the most heavily populated parts of the state, while keeping the results close in heavily populated counties that he lost.
Roosevelt performed much more strongly overall in South Jersey, winning majorities in six out of seven of the southernmost counties in the state; his strongest county win there was urban Camden County, where he broke 60% of the vote. In South Jersey, Willkie won only rural Cape May County. Besides his victories in North Jersey, Willkie also won Monmouth County and Ocean County in the central portion of the state.
New Jersey by 1940 had become a closely divided swing state with a Republican lean, and its results in 1940 adhered to that pattern. Roosevelt had carried the state in the midst of both of his preceding nationwide landslides, although only by a very narrow margin in 1932. As Roosevelt decisively won re-election to an unprecedented third term, carrying 38 out of 48 states, his narrow margin of victory in New Jersey made the state about 6% more Republican than the national average.