ADU rules in Peoria

A detached backyard cottage is not allowed in any of Peoria's ordinary residential zoning districts. UDC 5.4.2.A states that accessory structures and accessory storage buildings 'shall not be used as dwelling units,' and UDC 3.5.1 permits only one principal building per zoning lot outside multifamily developments, the Form Districts, and the commercial, office and industrial districts. The single real exception is the Heart of Peoria Form Districts, small mapped areas in the historic core: on R-4 frontage lots in Sheridan Triangle (6.2.D.8), Prospect Road (6.3.D.8) and West Main (6.4.H.8), and on West Main Local frontage lots (6.4.F.8), 'parking and accessory unit (maximum 650 square feet)' are permitted in the buildable area at the rear of the lot. The code never uses the phrase 'accessory dwelling unit' anywhere, and a full text search of the whole Code of Ordinances returns zero hits for it.

Peoria defines a 'Dwelling' as a building containing one or two dwelling units (10.3), so carving a basement or internal apartment out of a house creates a Two-Family (Duplex) use rather than an accessory unit. The permitted use table in 5.2 shows Two-Family permitted in RE and R1 through R8, but the use standard closes the conversion path in the low density districts: 5.3.1.A provides that 'a duplex, in the RE, R1, R2, and R3 Districts is permitted only when designated at the time of platting. A duplex, in the R-4 district, is permitted only as new construction.' R4 covers a large share of Peoria's older single family fabric: a Community Development staff presentation in the 2026-08-10 Land Bank Board packet counts 958 of the city's 1,100 land bank parcels as R4. In R5 through R8 a two unit conversion is permitted by right subject to the minimum lot area per unit in 4.2.4 (3,600 square feet per unit in R5, 2,900 in R6, 2,170 in R7, 1,089 in R8). In the Form Districts only the West Main Local frontage allows an internal second unit: 'One English basement unit or one accessory unit is permitted per lot' (6.4.F.8.a); Sheridan Triangle, Prospect Road and the other West Main frontages expressly prohibit conversion of a single family primary structure to multiple family use.

The only size cap the code attaches to an accessory dwelling sits in the Form Districts. UDC 6.6.1.H.1 states that 'the maximum floor area of an accessory unit shall be 650 square feet,' and each Form District frontage standard repeats the 650 square foot figure (6.2.D.8.a, 6.3.D.8.a, 6.4.F.8.b, 6.4.H.8.a). Outside the Form Districts there is no ADU size number because there is no ADU: 5.4.2.D caps a detached accessory storage building at 1,092 square feet (one building where the house has an attached garage, two where it does not, and never larger than the principal structure) and 4.2.4 caps accessory structure height at 14 feet in every residential district, but 5.4.2.A forbids using any of that floor area as a dwelling unit. A Form District accessory unit must also fit the district's building envelope standards and sit in the buildable area at the rear of the lot, behind a parking setback line 30 feet from the required building line.

Nothing in the UDC conditions a second unit on the owner living on the property. The Form District accessory unit standards (6.2.D.8, 6.3.D.8, 6.4.F.8, 6.4.H.8) impose no occupancy test, and the duplex standard in 5.3.1.A turns on platting and new construction rather than ownership. Owner occupancy only bites in two collateral programs. A short term rental is permitted by right in the Estate Residential and Single-Family Residential districts, and in the Form District R-4 and West Main Local frontages, only 'where the property is owner occupied by a natural person or persons' (5.3.1.B.1 and B.2). And City Code § 5-528(b) exempts 'owners who occupy single-family dwellings or duplexes' from the annual residential property registration. Illinois has no statewide ADU statute, so no state floor preempts or supplies a local owner occupancy rule here.

The citywide Parking Schedule in 8.1.6 requires, for Single and Two Family dwellings, '2 per unit for units constructed after June 4, 1991' (older units keep the pre-1991 standard of 1 per unit plus 1 for each permitted gratuitous guest). So a lawful second unit added by duplex conversion in R5 through R8 pulls two more off-street spaces. The Form Districts run on their own schedule: 8.1.6.A excludes them and points to 6.9, which requires 'a minimum of 1 and 1/8 parking space per residential unit,' of which 1/8 must be shared parking. Critically, 6.9.1.A waives minimum parking entirely on zoning lots under 7,500 square feet in Sheridan Triangle, Prospect Road and West Main (under 12,000 square feet in the Warehouse District), which covers most historic core lots. Form District parking may be satisfied on site or within 600 feet. PA 104-0457, Art. 5 (People Over Parking Act), effective 6-1-2026, bars any unit of local government from imposing or enforcing minimum automobile parking requirements on a development project (a permit to construct or reconstruct a dwelling qualifies) within one-half mile of a public transportation hub (any rail transit station, or an intersection of 2 or more bus routes with combined 15-minute peak frequency) or one-eighth mile of a 15-minute-peak bus corridor, binds home-rule units (Section 5-90), and grandfathers site plans approved before the effective date (Section 5-15(b)). Peoria has no rail transit station, so applicability turns on whether CityLink routes meet the act's 15-minute combined peak-frequency tests, which was not verified from schedules; where it applies, the act would override both the citywide two-space minimum and the Form District ratios for new construction.

Where an accessory unit is allowed at all, the review is administrative. UDC 2.2.1 provides that 'zoning review shall accompany all applications for a building permit or Development Review Board review,' and in the Form Districts the Development Review Board, a staff panel of Community Development, Public Works, Inspections, Police and Fire representatives (2.1.3.A), approves the site plan submitted with the building permit for permitted uses (2.1.3.B.2.b). No public hearing and no special use is involved. There is also no discretionary route to an accessory unit outside the Form Districts: 2.6.1.A limits variations to 'height, yard, bulk, lot area, and fence height provisions,' so the Zoning Board of Appeals cannot grant a use variance, and no accessory dwelling appears in the special use column of the 5.2 permitted use table. The remaining path is a rezoning to a district where two family or multifamily use is allowed, heard by the Planning and Zoning Commission and decided by City Council.

Peoria places no primary residence test, no separate sale rule and no length of tenancy floor on renting a lawful unit long term. Any residential dwelling the owner does not live in must be registered annually under City Code §§ 5-521 and 5-529 at $75 plus $20 per additional unit, with a designated local agent; § 5-528 exempts owner occupied single family dwellings and duplexes, family occupied properties, and properties listed for sale. Short term rental (under 30 consecutive days) is a separately regulated use: 5.3.1.B.1 permits it by right in the Estate Residential and Single-Family Residential districts only where owner occupied by a natural person, otherwise by special use; 5.3.1.B.2 permits it by right in the Form District R-4 and West Main Local frontages only where owner occupied, and not at all in other Form District property types. Operators need a short term rental license ($75 per unit per year), must remit the 8 percent hotel/motel room rental tax, and 5.3.1.B.6 provides that 'additional dwelling units cannot be added to the original design of the dwelling.' Special use short term rentals are further capped at 1 percent of the developed parcels in a neighborhood and must be 1,500 feet apart.