DuPage County, IL Zoning Overlays & Bonuses: Density Bonus Law (2026)

DuPage County's density bonus applies specifically inside the R-5 General Residence District under Zoning Ordinance Sec. 3. The base lot size table in the same section sets the yield a developer starts from: 8,000 square feet per lot for single-family detached dwellings, 10,000 square feet for two-family dwellings, and 5,000 square feet of land area per dwelling unit (15,000 square-foot minimum lot) for multiple-family dwellings. A property owner or developer who elects to build housing affordable to low and moderate income families earns a density bonus of one additional dwelling unit for each qualifying affordable unit constructed, but that bonus cannot exceed 25% of the number of dwelling units otherwise permitted on the zoning lot's actual area, calculated without any bonuses or conditional-use allowances.

S. Department of Housing and Urban Development requirements and guidelines governing the construction, operation and maintenance of low- and moderate-income housing. The code defines a qualifying affordable unit narrowly: it must be provided through the federal Section 8 Program or an equivalent federal program under which the income-restriction assistance stays attached to the unit for a minimum of 20 years, so a unit that loses its subsidy or affordability restriction before that term is not counted for bonus purposes. The provision traces to Ordinance T-4-05, adopted July 11, 2006, and was carried forward in the county's 2011 zoning rewrite under Ordinance T-2-11.