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O'Fallon, MO Building Setbacks & Zoning: Setback Rules (2026)

Some Restrictions
Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

Key Facts

R-1 front yard
25 feet minimum
R-1 side yard
6 feet each side
R-1 rear yard
25 feet minimum
AG District setbacks
50 ft front/rear, 30 ft sides
First zoning-violation fine
up to $200 (§ 100.010)

Summary

O'Fallon requires a minimum 25-foot front yard, 6-foot side yards and a 25-foot rear yard for every R-1 single-family lot, with wider margins in other districts: R-1A needs 40 feet front and rear, and the AG District needs 50 feet on all three sides. City Code § 400.080 sets the base standard most homeowners fall under.

D. Regulations And Performance Standards. The following regulations shall apply: ... 4. Yard Requirements. a. Front Yard. Not less than twenty-five (25) feet. b. Side Yards. Not less than six (6) feet on each side of the dwelling. c. Rear Yard. Not less than twenty-five (25) feet.

View official code

Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: rev 4860992; v58 updated 2026-05-14; through 05-14-2026).

Full Breakdown

O'Fallon's Zoning Code (Chapter 400) fixes yard setbacks district by district rather than with a single citywide number. 080(D)(4) requires a front yard of not less than twenty-five (25) feet, side yards of not less than six (6) feet on each side of the dwelling, and a rear yard of not less than twenty-five (25) feet; lot coverage in R-1 is capped at thirty-five percent (35%) and lots must be at least 10,000 square feet. 085 doubles the front and rear setbacks to forty (40) feet and requires twelve (12)-foot side yards, reflecting its 22,000-square-foot minimum lots.

130) requires a thirty (30)-foot front yard and twenty (20)-foot side yards. 155) requires the largest margins in the code: fifty (50) feet front and rear and thirty (30) feet on the sides, rising to fifty (50) feet on a corner lot. Every district's yard requirement applies to "every lot, building, or structure," and corner lots generally must observe the larger street-side setback rather than the standard interior side yard. Site plan review by the Planning and Zoning Commission is required before a building permit issues in most non-R-1/R-1A districts, giving the City a chance to confirm setback compliance before construction begins.

Violations & Fines

A structure built inside the required setback violates Chapter 400 of the Zoning Code. Under the City's general penalty provisions, § 100.010(A)(4), a municipal zoning violation under RSMo §§ 89.120 and 89.490 draws a maximum fine of $200 for a first offense within twelve months, rising to $275, $350 and $450 for the second, third and fourth-plus violations; the City can also require the encroaching structure to be moved or removed.

Frequently Asked Questions

What is the minimum front yard setback in O'Fallon's R-1 district?
City Code § 400.080(D)(4)(a) sets the R-1 front yard at not less than twenty-five (25) feet, with side yards of at least six (6) feet on each side of the dwelling and a rear yard of at least twenty-five (25) feet. These minimums apply to every lot, building or structure in the district, including corner lots facing a second street.
Do setbacks change in O'Fallon's AG Agricultural District?
Yes. Section 400.155(D)(4) requires a fifty (50)-foot front yard, thirty (30)-foot side yards (fifty feet on a corner lot) and a fifty (50)-foot rear yard, roughly double the R-1 standard, plus a mandatory hundred (100)-foot buffer between livestock structures or manure storage and any property line.
What happens if I build too close to my property line?
The City treats an undersized setback as a zoning violation under Chapter 400. Section 100.010(A)(4) caps the fine at $200 for a first offense in a twelve-month period, climbing to $450 for a fourth violation, and code enforcement can require the structure to be relocated or removed to bring the lot into compliance.
Are side-yard setbacks different for corner lots in O'Fallon?
Yes. In the R-1 District, a corner lot must provide the same twenty-five (25)-foot setback on its street-facing side yard that applies to a front yard, rather than the standard six (6)-foot interior side yard, per § 400.080(D)(4). Other districts, including C-1 and AG, apply similar wider corner-lot rules.

Sources & Official References

Other rules in O'Fallon

Noise Ordinances: Construction HoursSome RestrictionsFence Regulations: Height LimitsSome RestrictionsStructure Height LimitsSome RestrictionsLot Coverage LimitsSome RestrictionsFence Regulations: Material RestrictionsSignificant RestrictionsFence Regulations: Fence Permit RequirementsSome RestrictionsAnimal Ordinances: Pet Groomer RulesSome RestrictionsFire Regulations: Propane StorageSome Restrictions

All O'Fallon rules

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