It was around 11:15 a.m. when, they tell Action News, the sky darkened and a high funnel cloud appeared over the New Castle County Government Center at 87 Reads Way.
While the funnel cloud did not appear to touch the ground, high wind caused some minor damage to the roof of the building.
"All we saw was a white funnel cloud come down. It went over a transformer and it blew up like a firecracker," said Gerald Lodge.
The National Weather Service says it was a "straight line wind event with a funnel cloud," also called a microburst event.
A county vehicle and an employee's vehicle were damaged by falling tree limbs.
A New Castle County spokesman says there was also roof damage to the Gilliam Building.
There was no interior damage to either building, though the power did go out.
County government offices were still open.
No injuries were reported.