Building permits, zoning and septic rules in Mount Vernon, Illinois

At a glance

Building permits

Required for new structures, moving buildings, additions and structural alterations¹

Zoning

City zoning applies inside Mount Vernon²

Minimum home size

R-1 principal buildings: 1,200 square feet, excluding the garage⁵

Septic approval

State rules require plan approval from IDPH or the applicable local authority before construction⁴

Owner-builder

Qualifying owners may do their own plumbing, subject to code and inspection; local plumbing permits can still apply⁶⁷

Private wells

State rules require a permit before construction, modification or sealing⁸

Who to call

Contact details are copied from each office’s official page and were checked against it on October 12, 2026.

Do you need a building permit in Mount Vernon, IL?

Mount Vernon requires a building permit before a building or other structure is erected, moved, added to or structurally altered; parking and parking-lot improvements also require a building permit.¹ The city may issue a building permit only when the project conforms to zoning, unless the specified city approval process authorizes an exception.¹

Mount Vernon requires inspection of all permitted work, and building-permit fees depend on project cost.⁹ Before budgeting a house, addition or outbuilding, ask Engineering and Inspections for the applicable fee and inspection schedule.⁹

Who issues building permits in Mount Vernon, and how do you apply?

Mount Vernon Engineering and Inspections accepts building-permit applications online, by email to the building inspector or in person at City Hall.⁹ Contact the office at (618) 242-6830 or [email protected] for the application and project requirements.⁹

Illinois does not have the Capital Development Board issue building permits or conduct building-code inspections for privately funded construction; those requirements are addressed by local government.¹⁰¹¹ A qualifying owner may perform plumbing on a home intended for the owner’s own occupancy, but the work must meet the Illinois Plumbing Code and remains subject to inspection.⁶ Local plumbing-permit requirements can still apply.⁷

Does Mount Vernon have zoning, lot-size rules and setbacks?

Mount Vernon applies city zoning inside its corporate limits, with district regulations covering residential, agricultural, business, industrial and planned-development areas.²¹² The city says district rules determine permitted buildings, property uses, setbacks, height and lot size, so ask the Building Inspection Department to identify the district and standards for the actual parcel.¹³

In Mount Vernon’s R-1 Low Density Residential district, the minimum floor area for a principal building is 1,200 square feet excluding the garage.⁵ That minimum is district-specific.⁵ A zoning change does not replace a building permit or other required approvals.¹³

How do septic permits and private wells work in Mount Vernon?

Illinois requires plan approval from IDPH or the applicable local authority before construction of a new private sewage disposal system, and notification at least 48 hours before construction, installation, repair or modification begins.⁴ Jefferson County identifies its Health Department and Illinois EPA as private-sewage regulators; the Health Department offers onsite sewage and private-water-supply inspections.³¹⁴ Ask Environmental Health to confirm the administering office for a Mount Vernon address and ask the city whether public sewer connection is required.¹⁴¹³

Illinois also requires a permit from IDPH or an approved local health department before constructing, modifying or sealing a private well.⁸ A composting toilet does not remove the need to dispose of other domestic wastewater through a conventional private sewage disposal system under state rules.¹⁵

Can you live in an RV or tiny home in Mount Vernon?

We could not confirm Mount Vernon’s rules for residential RV occupancy, temporary camping, tiny homes or accessory dwelling units; ask the Building Inspection Department about the proposed dwelling and parcel before buying.¹³ For a tiny-home proposal in Mount Vernon’s R-1 district, the verified principal-building minimum is 1,200 square feet excluding the garage.⁵

Mount Vernon has separate rules for mobile homes and manufactured homes: mobile-home placement has inspection requirements and conditional inspection exceptions, while a manufactured home in a manufactured-home development cannot be occupied without a city Certificate of Occupancy.¹⁶¹⁷ Those provisions address those housing types; ask the city how the proposed unit will be classified.¹⁶¹⁷¹³

What are the steps before building a home in Mount Vernon?

1. Ask Mount Vernon’s Building Inspection Department to identify the parcel’s district, permitted use, lot-size standards and setbacks before preparing a layout.¹³
2. Resolve wastewater and water arrangements: obtain required septic plan approval and any private-well permit before that work starts, and ask the city about utility connections.⁴⁸¹³
3. Submit the city building-permit application online, by email or at Engineering and Inspections, then arrange inspections for permitted work.⁹

For land outside Mount Vernon, consult the Jefferson County guide and confirm the jurisdiction with the city: Mount Vernon says its zoning oversight extends up to 1.5 miles beyond city limits.¹³ Before purchase, also ask the city about floodplain development and driveway access; we could not confirm the applicable city requirements.¹³

Watch-outs

• Mount Vernon’s R-1 minimum floor area excludes the garage; do not count garage space toward the dwelling minimum.⁵
• A qualifying owner’s plumbing exemption does not establish an exemption from Mount Vernon building permits or local plumbing permits.⁶⁷¹
• We could not confirm Mount Vernon’s RV occupancy or temporary-camping rules; ask the Building Inspection Department before planning to live onsite during construction.¹³

Sources

1. § 161.086 Building Permits Required (Mount Vernon), quoted and re-checked
2. § 161.003 Territorial Limits of Ordinance (Mount Vernon), quoted and re-checked
3. jeffersoncounty.illinois.gov, quoted and re-checked
4. 77 Ill. Adm. Code 905.190 Installation Approval (Illinois statewide rule), quoted and re-checked
5. § 161.314 R-1 Low Density Residential (Mount Vernon), quoted and re-checked
6. HB5913 Enrolled — Illinois Plumbing License Law amendment (Illinois statewide rule), quoted and re-checked
7. 225 ILCS 320/18 — Local regulation; Department standards (Illinois statewide rule), quoted and re-checked
8. 77 Ill. Admin. Code 920.130, Water Well Permit Requirements (Illinois statewide rule), quoted and re-checked
9. Mount Vernon Engineering and Inspections (mtvernon.com)
10. Illinois Codes FAQ (Illinois statewide rule), quoted and re-checked
11. Illinois Codes FAQ (Illinois statewide rule), quoted and re-checked
12. § 161.006 Schedule of District Regulations (Mount Vernon), quoted and re-checked
13. Mount Vernon Building Inspection Department — Zoning Assistance (mtvernon.com)
14. Jefferson County Health Department — Environmental Health (jeffersoncountyhealthdept.org)
15. 77 Ill. Adm. Code 905.130 Human Waste Disposal (Illinois statewide rule), quoted and re-checked
16. § 156.03 Building Permit and Inspection (Mount Vernon), quoted and re-checked
17. § 157.03 Building Permit, Inspection and Certificate of Occupancy for Manufactured Home (Mount Vernon), quoted and re-checked

Written October 12, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.