Building at Belle Vue would be a loss to the community, said protesters
Preferred sites have been earmarked for three County Durham "super schools".
Consett's academy will be built on the Belle Vue site, Stanley's at the former Kings Head sports field, and the Durham City academy on Belmont School's site.
The choice of Belle Vue will anger many local residents, 1,100 of whom signed a petition arguing that the area is a vital community green space.
But the county council's cabinet said the site offered the best access and potential for regeneration.
The proposed Durham City academy - sponsored by a Durham University-led consortium - will have 1,200 places, replacing Belmont School and Durham Gilesgate College.
Stanley's 1,800-pupil academy, sponsored by New College Durham, is set to replace Stanley School of Technology, Greencroft Business and Enterprise Community School.
The Consett academy, also backed by the Durham University consortium, would cater for 1,500 students in place of Moorside Community Technology College and Consett Community Sports College.
On Thursday, opponents to Consett's Belle View option protested outside County Hall, arguing that building on the area - which is used by children and dog walkers - would be a loss to the community.
Speaking after the cabinet meeting, councillor Clive Robson, who represents Consett North, said: "We are confident and satisfied that we will provide first class leisure facilities and more useable hours of outdoor provision for the whole community."