Robert Weiner was defeated in his bid for another term on the New Castle County Council,
Dee Durham, who formerly led Preservation Delaware, defeated the long-time Republican member of the council.
Durham claimed Weiner had not worked hard enough to preserve open space in his district in the Brandywine Hundred area of northern New Castle County.
A recent bone of contention among residents of the area was the Brandywine County Club property, which was partially rezoned for residential and apartment development.
Activists were also unhappy with the development of a new campus for Wilmington University across from Concord Mall. They claimed the property was too close to other open space and National Park space.
Weiner, a retired lawyer, had served as a Republican member of the County Council for decades and had been active on the development front.
Weiner had supported the Unified Development Code, which according to critics brought lengthy and costly delays for projects and shifted growth and sprawl to the Middletown area.
Efforts have been made of late to reduce the delays in cases where the project brings jobs or meets code requirements.