The county's zoning board of appeals voted 5-to-2 last week against building the mosque. The majority cited traffic congestion and an oversaturation of religious institutions in the area.
On Wednesday, Muslim, Christian and Jewish officials said all faiths have a constitutional right to worship freely.
"There is no meaning to the free exercise of religion if you cannot have a place for sacred assembly and congregation, a place for worship," said Dr. Zaher Sahloul, Council Of Islamic Organizations.
"An injustice to one faith is an injustice to all who have faith," said Rev. Michael Mann, United Methodist Church. "I pray that the DuPage County Board may take efforts to reverse this decision."
The county's development committee will review the matter, which then goes to the DuPage County Board.