It's part of the Port Authority's $8 billion project to transform the airport.
The new Delta concourse is located on the far eastern end of Terminal C and will have seven new gates starting Monday.
Eventually, all four concourses will have one centralized security checkpoint.
Gov. Andrew Cuomo pointed out renovations continue even though some claimed it was impossible while keeping it in operation.
"But that is a theory that stymies construction and growth. That is a theory that is totally repugnant to the New York way," he said. "New York always did the impossible. We were built on the impossible."
The eastern side of the new Delta terminal offers views of Flushing Bay and Citi Field.
Delta is the largest airline at LaGuardia with 275 flights every day.
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