Zoning expanded single-family land share and raised lot sizes
A Federal Reserve Bank of Philadelphia working paper shows that historical zoning regulations in Cook County systematically expanded single-family land use while reducing apartments and mixed-use commercial space between 1921 and 1980. Prewar minimum lot sizes increased lot areas by 20 percent.
Dividing the greenfield grid
Analyzing a new panel dataset of zoning maps and bylaws across 120 Cook County municipalities from 1921 to 1980, researchers evaluated land that was undeveloped prior to regulation.
Unregulated suburban development set aside 63 percent of land for single-family homes, 18 percent for apartments, and 11 percent for commercial uses.
Under comprehensive zoning, post-regulation development shifted to 83 percent single-family homes, 5 percent apartments, and 7 percent commercial space.
Adopting the most flexible zoning observed reduced single-family land coverage by 44 percentage points while reallocating space to businesses and apartments.
The median post-zoning suburb reserved 93 percent of land exclusively for single-family housing.
Decades between plat and property
Minimum lot size rules bound development earlier than previously recognized.
Between 1921 and 1945, zoning added 1,619 square feet to average lots, a 20 percent expansion over unregulated outcomes.
Required median lot sizes grew from 5,000 square feet in the 1920s to 7,500 square feet by the 1970s.
The data reveals an average 27-year lag between land subdivision and house construction.
Over half of homes built in the 1950s occupied parcels platted in the 1920s, demonstrating that municipal rules often crystallized earlier private subdivision designs.
Rigid mandates outlast markets
The paper convincingly proves that early zoning reshaped American suburbs far beyond private market forces alone.
Methodologically, it exposes major flaws in standard studies that fail to track historical parcel subdivision dates.
These long-run findings highlight how past regulatory choices actively restrict current housing supply reforms.
Source: Zoning and the American Suburb
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