This is a research dataset, not a ranking. It tracks the current county-level ADU framework or 2026 transition status for all 24 Maryland county-level jurisdictions, including Baltimore City. Each row links to an official source and shows when that status was last verified.
Dataset snapshot: September 19, 2026 · Coverage: 24 county-level jurisdictions · Underlying research database: 272 structured rule records, 259 marked verified. Five rapidly changing jurisdictions were rechecked on September 19.
How to read the status
Verified means we located and checked an official source supporting the status shown. Needs review means a current local code or framework was located, but the 2026 state-conformity / transition status has not yet been fully verified from a current official source. “Needs review” does not mean ADUs are prohibited or that a jurisdiction is out of compliance.
| Jurisdiction | Current framework / transition status | Framework class | Size rule | Parking | Owner occupancy | Verification | Effective date recorded | Primary official source |
|---|---|---|---|---|---|---|---|---|
| Allegany County Local guide → | Current local code found, 2026 state-conformity status still needs review | Legacy / needs review | No single countywide 2026 ADU cap verified; current code uses separate accessory-apartment and ADU categories | No residential-ADU-specific parking rule is cleanly established under the split current categories; general parking standards vary by use. Confirm classification with County zoning. | No countywide residential owner-occupancy rule is cleanly established under the split current categories; confirm which use category applies. | Needs review — | — | Allegany County zoning code ↗ |
| Anne Arundel County Local guide → | Existing ADU framework remains in effect; Bill 61-26 is amended and scheduled for a September 21 hearing. | Active + pending amendment | Current detached rule: lesser of 800 sq ft or 50% of principal dwelling floor area; 2026 amendment pending | No additional ADU spaces under current guidance | No general current owner-occupancy rule normalized; owner occupancy affects short-term-rental eligibility | Verified 2026-09-19 | — | Anne Arundel County — Bill 61-26 ↗ |
| Baltimore City Local guide → | Bill 26-0195 remains in committee after the September 17 public hearing. | Pending 2026 law | Proposed: no greater than 75% of principal dwelling floor area | Draft parking rule not normalized; bill is pending | Draft owner-occupancy rule not normalized; bill is pending | Verified 2026-09-19 | — | Baltimore City Legistar — Bill 26-0195 ↗ |
| Baltimore County Local guide → | Legacy accessory-apartment framework current, 2026 conformity status needs review | Legacy / needs review | Interior: up to 1/3 and 2,000 sq ft; detached: 800 sq ft on lots under 1 acre or 1,200 sq ft on lots 1+ acre | No separate ADU-specific parking minimum is stated in the current §400.4 accessory-apartment framework reviewed; confirm general residential parking with PAI. | Required under current accessory-apartment framework | Needs review — | — | Baltimore County zoning ↗ |
| Calvert County Local guide → | Current 2026 local ADU code verified | Active / current 2026 | Up to 75% of principal single-family dwelling gross floor area | Default 1 additional off-street space; waiver path available | Required | Verified 2026-09-17 | — | Calvert County Zoning Ordinance Article 18 ↗ |
| Caroline County Local guide → | Current local ADU code present, 2026 conformity review pending | Legacy / alignment review | Current local cap: 50% of principal dwelling and 1,000 sq ft | Adequate parking for the ADU and all other uses must be provided | Required | Needs review 2026-09-17 | — | Caroline County Zoning Code Article IX ↗ |
| Carroll County Local guide → | ADU conformity amendments remain proposed after the September 3 public hearing; no adopted ADU ordinance is shown on the current adopted-ordinance list. | Pending 2026 amendments | Varies by district/type: residential attached 800 sq ft; agricultural attached 1,000 sq ft; detached route differs | Varies: 2 spaces for residential attached; 1 space per bedroom in agricultural conservation | Required under current framework | Verified 2026-09-19 | — | Carroll County — ADU text amendments ↗ |
| Cecil County Local guide → | 2026 local ADU framework status needs review | Legacy / alignment review | Interior: max 30% of principal dwelling GFA; accessory-building unit: max 50% of accessory structure | Off-street parking must comply with Article XIV | Required | Needs review — | — | Maryland Department of Planning ADU page ↗ |
| Charles County Local guide → | 2026 conformity law adopted and effective | Active / enacted 2026 | Under 3 acres: lesser of 1,000 sq ft or 75% of principal dwelling floor area; 3+ acres: 75% | No additional off-street spaces for the single-family-detached ADU use | No controlling owner-occupancy condition was verified in the enacted 2026 materials reviewed; confirm the planned use with the Zoning Administrator. | Verified 2026-09-17 | 2026-08-21 | Charles County Bill 2026-06 enactment ↗ |
| Dorchester County Local guide → | Current local accessory-apartment code present, 2026 conformity status needs review | Legacy / alignment review | Lesser of 800 sq ft or one-third of the building | 1 additional space | Required | Needs review — | — | Dorchester County zoning code ↗ |
| Frederick County Local guide → | Existing local ADU framework verified, 2026 conformity review pending | Active legacy + pending 2026 bill | Current framework includes 50% size limits; units at or below 1,000 sq ft use a different approval route from larger units | 1 additional space under current rules | Required under current rules | Verified 2026-09-17 | — | Frederick County Zoning ↗ |
| Garrett County Local guide → | Current zoning references ADUs, detailed 2026 conformity status needs review | Special jurisdiction | No single countywide rule; depends on Deep Creek zoning, a municipality, or an unzoned area | No single countywide rule | No single countywide rule | Needs review — | — | Garrett County zoning definitions ↗ |
| Harford County Local guide → | Existing local ADU framework present, 2026 conformity status needs review | Legacy / alignment review | 300–1,500 sq ft; current record also caps size at 50% of primary habitable area | 1 additional off-street space under the current ADU rule | Required | Needs review — | — | Harford County Zoning Code ↗ |
| Howard County Local guide → | 2026 local ADU framework verified current | Active / current 2026 | Up to 75% of principal dwelling exterior footprint | 3 off-street spaces under current guidance, with exceptions | Required | Verified 2026-09-17 | 2026-04-08 | Howard County ADUs ↗ |
| Kent County Local guide → | Existing local ADU code present, 2026 conformity review pending | Legacy / alignment review | Must remain subordinate in size and appearance; no numeric countywide cap normalized | 1 space | Required | Needs review — | — | Kent County Land Use Ordinance ↗ |
| Montgomery County Local guide → | Existing local ADU licensing and zoning framework verified current | Active + 2026 transition | Detached: least of 50% of principal dwelling footprint, 10% of lot area, or 1,200 sq ft | 0 within 1 mile of rail; otherwise 1 or 2 on-site spaces depending on driveway; waiver available | Required under current framework | Verified 2026-09-17 | — | Montgomery County Accessory Dwelling Unit Class 3 License ↗ |
| Prince George’s County Local guide → | CB-074-2026 remains in committee / pending; current Legistar status is To Committee. | Pending 2026 bills | Do not rely on draft size provisions yet; county bills remain pending | Do not rely on draft parking provisions yet; county bills remain pending | Not final; county bills remain pending | Verified 2026-09-19 | — | Prince George’s County Council — CB-074-2026 ↗ |
| Queen Anne’s County Local guide → | Planning Commission-sponsored Ordinance 26-15 is pending and can be introduced / scheduled for a public hearing at the September 21 County Commissioner meeting. | Legacy + pending 2026 ordinance | Current legacy cap: 1,500 sq ft; Ordinance 26-15 would replace the legacy framework | No ADU-specific parking minimum is stated in current §18:1-48; general parking rules may still apply. Proposed Ordinance 26-15 is pending. | Required under current legacy rule | Verified 2026-09-19 | — | Current §18:1-48 ↗ Sept. 21 Ordinance 26-15 agenda ↗ |
| Somerset County Local guide → | Existing local ADU code present, 2026 conformity status needs review | Legacy / alignment review | Current local cap: 50% of principal living area | 0 if existing house has adequate on-street parking; otherwise 1 additional space | Required | Needs review — | — | Somerset County zoning ordinance ↗ |
| St. Mary’s County Local guide → | Existing local ADU framework present, 2026 conformity status needs review | Legacy / alignment review | Attached: lesser of 40% of principal GFA or 900 sq ft; detached: lesser of 40% of accessory-structure GFA or 900 sq ft | 1 additional independently accessible space | Required | Needs review — | — | St Mary County ↗ |
| Talbot County Local guide → | Existing local ADU code verified current, 2026 conformity review pending | Legacy / alignment review | Interior: lesser of 35% of primary GFA or 900 sq ft; detached: 900 sq ft with separate lot-size rules | 1 space per accessory apartment | Required for internal ADU; rental rules vary by form | Verified 2026-09-17 | — | Talbot County Code Article IV ↗ |
| Washington County Local guide → | ADU ordinance adopted as ORD-2025-33 | Active / enacted | Lesser of 75% of primary dwelling GFA or 1,200 sq ft; basement/attic exception applies | 1 additional space; waived within ½ mile of a transit stop | No owner-occupancy requirement identified in ORD-2025-33 | Verified 2026-09-17 | — | Washington County Local Legal Materials ↗ |
| Wicomico County Local guide → | 2026 ADU bill adopted, effective October 19 2026 | Enacted / future effective | Current until Oct. 19: legacy 50% rule. Bill 2026-08 also uses 50%, creating a conflict with state 75% guidance | Current legacy process until Oct. 19; Bill 2026-08 then requires 1 space per bedroom, with waiver issue unresolved | Required under current legacy rule; Bill 2026-08 removes owner-occupied language Oct. 19 | Verified 2026-09-17 | 2026-10-19 | Wicomico County Legislative Bill 2026-08 ↗ |
| Worcester County Local guide → | Existing local accessory-apartment code verified current, 2026 conformity review pending | Legacy / alignment review | Lesser of 35% of principal dwelling GFA or 900 sq ft | 1 additional off-street space | Not required; former requirement repealed in 2020 | Verified 2026-09-17 | — | Worcester County Zoning Code ZS 1-338 ↗ |
Methodology and limitations
The public table is generated from our structured Maryland ADU research database. We prioritize official county/city code, legislation, planning and zoning pages, meeting records and Maryland state sources. The database stores the source URL, source title, verification state, effective date when known, and verification timestamp alongside individual rule records.
This version normalizes four homeowner-facing fields across all 24 county-level jurisdictions: framework class, size rule, parking and owner occupancy. Where the available official record does not support a clean statewide comparison, the cell explains the exact limitation—for example, a split use category, district-specific rule, pending legislation, or a condition that should be confirmed with the local zoning office. Pending legislation is kept separate from current effective law.
Municipalities such as Annapolis, Rockville, Gaithersburg, Salisbury and others can have separate zoning authority and are not represented as independent rows in this county-level dataset yet. Use the Jurisdiction Finder and Rules Tracker for municipal research.
If an official source conflicts with this table, the official source controls. Please send corrections through our correction process; our Editorial & Research Policy explains how we verify and update regulatory information.
What to do next
Start by finding the office that reviews your property. A mailing city or a county guide does not establish your parcel’s authority.
- Find Who Reviews My Property.
- Obtain your parcel identifier, survey, floor plans and utility records.
- Ask the reviewing office which current rules, supporting documents and approvals apply.
- Continue to your planning workspace.
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