Short answer: About 6% of the Town of Smithtown's land is inside an active sewer district on the county map, mostly Hauppauge Industrial Sewer District; about 37,526 of 39,466 one-family lots in the town's hamlets and villages sit outside any active sewer district. There is no town septic rebate, so the county and state grants are the funding.
Last updated: November 2026. Data computed 2026-11-07 from Suffolk County GIS; rules and programs re-read November 7, 2026.
Town of Smithtown in numbers
| Land in active sewer districts | 6% |
|---|---|
| Land in proposed districts | 1% |
| Places with ~0% active sewer | 4 of 9 hamlets and villages |
| One-family lots outside active districts | about 37,526 of 39,466 |
| Groundwater zones (land share) | Zone VIII about 51%; Zone I about 49% |
| I/A systems installed (Oct 2024) | about 126, 2% of the county's 5,344; 8th of the ten towns |
| Town septic rebate | No |
| Town code on I/A systems | None found beyond the county rules |
Sewer districts and where the cesspools are
- Active districts (7): Hauppauge Industrial Sewer District (about 4%), Hauppauge Municipal Sewer District (about 1%), Wind Watch Sewer District (about 1%), Kings Park Sewer District (under 1%), plus 3 smaller.
- Proposed districts (4 polygons): Smithtown Collection System Boundary (about 1%), Zone 1 (under 1%), Lake Avenue Sewer Extension (under 1%), plus 1 smaller. Homes inside a proposed district are excluded from the county and state septic grants.
By one-family lot count, the most lots outside an active district are in Commack (about 10,871), Smithtown (about 7,597), Hauppauge (about 5,240), Kings Park (about 4,702), St. James (about 3,823). Median one-family lots run from 0.24 acres in Kings Park to 2.04 acres in Nissequogue. In 5 of 9 places the median lot is smaller than Article 6's minimum for a new home on an on-site system in its main zone. Across the town, about 2% of the land is in FEMA's 1%-annual-chance flood zone; 1% is in a Special Groundwater Protection Area.
What the Town of Smithtown adds
- Rebate: none listed by the county as of November 7, 2026.
- Town code: no town-wide I/A mandate found beyond the county rules as of November 7, 2026.
- Building department: Town of Smithtown; villages with their own: Head of the Harbor, Nissequogue, The Branch.
Every hamlet and village in the Town of Smithtown
Land-area shares inside county sewer-district polygons; zone = main Article 6 groundwater zone; flood = FEMA 1%-annual-chance zone; lot = median one-family lot (acres). Linked names have their own page. Some village-run systems are missing from the county layer. Full table: sewer coverage by hamlet.
| Hamlet / village | Active sewer | Proposed sewer | Zone | Flood | Median lot (ac) |
|---|---|---|---|---|---|
| Commack | 3% | 0% | Zone I | 0% | 0.29 |
| Hauppauge | 26% | under 1% | Zone I | 0% | 0.34 |
| Head of the Harbor (village) | 0% | 0% | Zone VIII | 2% | 2.02 |
| Kings Park | 5% | 2% | Zone VIII | 2% | 0.24 |
| Nesconset | 3% | 4% | Zone I | 0% | 0.32 |
| Nissequogue (village) | 0% | 0% | Zone VIII | 16% | 2.04 |
| Smithtown | under 1% | 2% | Zone VIII | 2% | 0.49 |
| St. James | 4% | 2% | Zone VIII | 0% | 0.27 |
| Village of the Branch (village) | 0% | 12% | Zone VIII | 7% | 0.51 |
County rules apply on top: no cesspool-for-cesspool replacement since July 1, 2019, and an I/A system for new homes and major reconstruction since July 1, 2021. Details, licensing and grants: Suffolk County overview.
Frequently asked questions
How much of the Town of Smithtown is on sewer?
About 6% of the land in the town's hamlets and villages is inside an active county sewer district, and 1% inside proposed districts; about 37,526 of 39,466 one-family lots in the town's hamlets and villages sit outside any active sewer district. A district boundary is not a connection.
Does the Town of Smithtown have a septic rebate?
No town rebate is listed by Suffolk County as of November 7, 2026. Smithtown homeowners use the county grant (up to $20,000) and the state grant (up to $25,000); the town had about 126 I/A systems by October 2024.
Who issues building permits for septic work in Smithtown?
The Town of Smithtown building department, except in the incorporated villages (Head of the Harbor, Nissequogue, The Branch), which run their own. SCDHS approves the sanitary system itself.
Sources
Each source was re-read on November 7, 2026. Program amounts and rules change; the agency page is the authority.
- Suffolk County GIS Viewer map service (hamlets, villages, sewer districts, groundwater zones, flood zones, tax parcels)
- Suffolk County DHS presentation, 11/19/2024 (hosted by the Town of Shelter Island)
- Suffolk County DHS: Changes to wastewater practices effective July 1, 2019
- Suffolk County: Septic Improvement Program information
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