UNC officials presented the board with the plan for the development of the 979-acre Horace Williams land tract, which is expected to include research, commercial and residential facilities.
The commissioners cited county concerns, such as transportation and school growth, as key factors UNC officials should consider when planning the proposed expansion.
Commissioner Stephen Halkiotis said he is concerned that large-scale growth at the University would bring new students to Orange County schools.
"The county commissioners have a legal responsibility to provide schools," Halkiotis said.
"Please keep in mind that what you do has an impact on what we have a legal mandate to do."
Commissioner Barry Jacobs said he is concerned that the development does not place enough emphasis on mass transit use but instead would allow commuters to use their own vehicles with limited restrictions.
"This still seems like 20th-century thinking about transit," he said.
Jack Evans, a professor in the Kenan-Flagler Business School and special assistant to the chancellor, presented the proposal to the commissioners and said he recognizes these concerns.
But Evans also said the expansion is still in the early stages of planning and that the impact on schools or transit could not yet be determined.