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.
Original dataset snapshot: September 19, 2026 · Coverage: 24 county-level jurisdictions. The original snapshot described 272 structured rule records, 259 marked verified, and five rapidly changing jurisdictions rechecked that day. Selected rows have since received individually dated updates; those updates are not a complete October re-verification of all jurisdictions or of the original database counts. Read each row’s verification date, status and source notes. The CSV exports the table currently displayed.
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 → | Bill 61-26 remains pending: amended October 5, with the next hearing October 19. The Council record checked October 10 lists no final passage or effective date; proposed changes are not current law. | 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 was recommended favorably with amendment September 24, then re-referred to committee September 28. The October 10 review shows In Committee with no enactment number; the next hearing is October 22 at 9:00 AM. | 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 2026-10-08 | — | 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 → | Ordinance 2026-11 signed text supplied October 4. October 5 County reply confirms September 17 adoption; September 17 versus September 27 effective date remains unresolved. | Adopted; exact effective date unresolved | 75% of above-ground living area; attached/detached footprint also capped at 75% of primary dwelling footprint (§158.177(K)–(L)) | No separate ADU off-street requirement (§158.177(F)) | Owner must occupy primary or detached dwelling; confirm internal/attached interpretation (§158.177(B)) | Signed text and October 5 reply reviewed 2026-10-10 | September 17 or 27, 2026 unresolved after October 5 County reply | Ordinance evidence and source notes → |
| 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 | Charles County Planning Supervisor Joel Binkley confirmed on September 22, 2026 that no owner-occupancy rules were adopted as part of Bill 2026-06. | Verified 2026-09-22 | 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 → | CB 3-2026 effective; official parking sources conflict | Active framework / parking source conflict | Up to 75% of principal dwelling exterior footprint | Source conflict checked October 10, 2026: signed final CB 3-2026 §133.0.D.1.a shows 1.0 additional ADU space, while the DPZ portal states 3 spaces. Confirm the currently codified and enforced standard with DPZ; do not design from either number alone. | Required | Needs review 2026-09-17 | 2026-04-08 | Howard County ADUs ↗ Signed final CB 3-2026, §133.0.D.1.a ↗ Parking conflict and source notes → |
| 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 → | Signed Ordinance 20-36 (ZTA 26-06), adopted September 15, 2026, is effective October 5. Bill 41-26 remains pending. October 22 review covered zoning and bill status; licensing procedures and fees were not fully re-audited. | Effective zoning + pending licensing bill | General rule: ADU no larger than 75% of the primary single-family detached dwelling. Confirm measurement with DPS. A detached structure legally built before May 31, 2012 retains a setback/floor-area exception if not enlarged in size or height and no new windows are added on the wall nearest an abutting property; confirm exception treatment. Overall lot coverage still applies. | No extra ADU space within 1 mile of Metrorail, Purple Line or MARC. Otherwise 1 ADU space plus any required main-dwelling parking, unless Hearing Examiner waiver approved. If the main dwelling has no existing on-site parking, only the ADU space is required. | Owner occupancy remains required under current Class 3 licensing; Bill 41-26’s proposed repeal is pending. | Zoning and bill status reviewed 2026-10-22 | 2026-10-05 | Signed Ordinance 20-36 / ZTA 26-06 ↗ October 2026 DPS ADU guidance ↗ Bill 41-26 status ↗ |
| Prince George’s County Local guide → | CB-074-2026 was enacted September 29. Council lists November 16 as the effective date, with a commencement discrepancy requiring confirmation. CB-092-2026 remains pending. The September 23 staff statement predates enactment; confirm the current application path with DPIE. | Enacted zoning; not yet effective | Enacted text: maximum 75% of principal dwelling gross floor area; not yet effective | Current application parking requirements need confirmation | Enacted text requires principal dwelling or ADU owner-occupancy; not yet effective | Verified 2026-10-08 | — | Prince George’s County Council — CB-074-2026 ↗ |
| Queen Anne’s County Local guide → | Planning Commission-sponsored Ordinance 26-15 remains pending. The September 21 County Commissioner agenda placed it at the introduction / public-hearing-scheduling stage; no later adoption or effective date has been verified. | Legacy + pending 2026 ordinance | Current legacy cap: 1,500 sq ft; Ordinance 26-15 would replace the legacy framework | Current §18:1-48 has no parking requirement, according to Queen Anne’s County Planning and Zoning staff. Proposed Ordinance 26-15 remains 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
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