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Harrison County, MS Accessory Structures: ADU Rules (2026)

Significant Restrictions

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

ADU rules in Harrison County, MS, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Permit required: Conditional use permit
Reviewing body: Harrison County Planning Commission
Section: UDC § 812
Districts: Only where listed as conditional in § 415
Square footage exemption: Excluded from § 815.01 accessory building cap

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Mississippi under recent ADU streamlining laws. The Harrison County, MS rules below cover local size, height, and setback requirements.

Summary

A secondary living unit, a garage apartment or in-law suite, is allowed on a single-family lot in unincorporated Harrison County only with a conditional use permit; Section 812 of the Unified Development Code treats it as an accessory structure to the principal detached dwelling, in districts listed in Section 415.

These county ordinances apply to unincorporated areas of Harrison County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

A secondary living unit shall be allowed by a conditional use permit as an accessory structure to the principal detached single household dwelling in those zoning districts specified in Section 415.

View official code

Official source re-checked September 7, 2026: the cited page had not changed since it was quoted.

Full Breakdown

' That means a homeowner can't simply build or convert a garage apartment or in-law suite as of right, the use has to go through the county's conditional use process, reviewed and approved by the Planning Commission under Article XIV, Section 1404, in whichever zoning districts Section 415's Table of Uses lists the use as conditional. 06 requires that any building intended for use as a temporary or permanent dwelling meet the secondary living unit standards of Section 812 before it can be occupied as such, a structure built as a garage or storage building can't simply be converted to a dwelling without going through that conditional use approval first.

Violations & Fines

Occupying or converting a garage, accessory building, or other structure into a livable secondary unit without an approved conditional use permit under Section 812 is a zoning violation; the Harrison County Planning Commission can deny or revoke the permit, and the county can require the structure to be vacated or restored to non-dwelling use until the conditional use approval is obtained.

Frequently Asked Questions

Can I build an in-law suite or garage apartment on my property in unincorporated Harrison County?

Only with a conditional use permit. Section 812 of the Unified Development Code allows a secondary living unit as an accessory structure to a principal detached single-family home, but only in the zoning districts where Section 415's Table of Uses lists it as a conditional use, and only after Planning Commission approval.

Does a secondary living unit count against my accessory building size limit?

No. Section 815.01 specifically excludes a secondary living unit permitted under Section 812 from the cumulative square-footage calculation that otherwise caps all accessory buildings on a lot at the square footage of the primary residence.

Can I just convert my detached garage into a rental apartment without a permit?

No. Section 815.06 requires any building intended as a temporary or permanent dwelling to meet the Section 812 secondary living unit standards, which means going through the conditional use permit process, before it can legally be used as living space.

Sources & Official References

[1]Harrison County Unified Development Code

Other rules in Harrison County

Animal Ordinances: Chickens & LivestockSome Restrictions Fence Regulations: Height LimitsSome Restrictions Shed & Carport RulesSome Restrictions Parking Rules: Loading ZonesSome Restrictions Parking Rules: Driveway RulesSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Fence Regulations: Material RestrictionsSignificant Restrictions

All Harrison County rules

How Harrison County compares: Easiest Cities to Build an ADU·Compare Harrison County to another location·View the Mississippi accessory structures overview

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