Cesspool & Septic Service in Islip, NY: Sewer, Rules, Grants

Short answer: About 92% of Islip's land falls inside Southwest Sewer District, an active district on the county map.

Islip in numbers

Town	Town of Islip
Area	4.76 sq mi
In active sewer district	92% · Southwest Sewer District
In proposed district	0%
Groundwater zone	Zone VII 100%
FEMA flood zone	9%
One-family lots / median	4,408 / 0.26 ac
One-family lots outside active sewer districts	about 152

Computed 2026-11-07 from Suffolk County GIS (hamlet boundaries, sewer districts, groundwater management zones, FEMA flood zones, protection areas, tax parcels). Shares are of land area; a district boundary is not a hookup, and some village-run systems are missing from the county layer. Method and full table.

Sewer coverage

About 92% of Islip's land falls inside Southwest Sewer District, an active district on the county map. That still leaves pockets of Islip where homes were never connected and run cesspools or septic tanks. By parcel count, roughly 152 of Islip's 4,408 one-family lots sit outside an active district; that is the local cesspool and septic population, before counting unconnected lots inside districts. Neighbouring areas: Bay Shore (96% sewered, median lot 0.22 ac); East Islip (92% sewered, median lot 0.26 ac); Islip Terrace (69% sewered, median lot 0.25 ac). By active-sewer share Islip ranks 12 of the 165 Suffolk hamlets and villages we measured.

Groundwater, lots and flood exposure

Groundwater management Zone VII: Article 6's minimum lot for a new home on an on-site system here is 20,000 sq ft, unless the density is met another way or an exemption applies. County parcel records show 4,408 one-family lots touching Islip, with a median of 0.26 acres (about 11,300 sq ft), below that minimum and the 123rd-largest median lot in our Suffolk table. 9% of the land is in FEMA's 1%-annual-chance flood zone.

If your Islip street isn't connected, the same county replacement and grant rules apply as anywhere in Suffolk.

Who handles what in Islip

Building and electrical permits: Town of Islip
Sewer: Southwest Sewer District
System approvals and grants: SCDHS, 631-852-5700 (permits) / 631-852-5811 (grants)

Frequently asked questions

Is Islip on public sewer?

Mostly: about 92% of Islip's land is inside Southwest Sewer District, but not every home inside a district is connected.

Can Islip homeowners get septic grants?

Yes, if the home isn't sewered and isn't in a proposed sewer district: up to $20,000 from Suffolk and up to $25,000 from the state.

County rules, licensing and grant steps: Town of Islip overview, septic grants, replacement rules. More in Islip: Bay Shore, Central Islip, Brentwood, Oakdale.

Sources

Each source was re-read on November 7, 2026. Program amounts and rules change; the agency page is the authority.

Need cesspool or septic work in Islip?

Submit a request with your address. We match it to an independent, licensed Suffolk County operator who serves that address; the operator confirms the time and price with you.

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