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A Message from the Supervisor

“Welcome to Islip, the 3rd largest town in New York State, but with an endearing small town feel. We are so proud of our town…our beaches, golf courses, marinas, parks, housing opportunities for all, businesses, industrial parks, healthcare and educational institutions including our own Islip MacArthur Airport that provides many job opportunities. I sincerely hope you find this website helpful.” Angie


The Assessor's Office is available to assist you in any way possible with their assessment policies and procedures. Please note the following important dates:
  • Finalization of the Tentative Assessment Roll – On or before May 1, 2023.
  • GRIEVANCE DAY – Tuesday, May 16, 2023:

    9:00 am - 11:00 am | 2:00 pm - 4:00 pm | 7:00 pm - 9:00 pm

  • Finalization of the Final Assessment Roll – On or about July 1, 2023.

Change in Assessment Notices

On or before May 1, 2023, our office will mail change in assessment notices for all properties that experienced an increase or decrease in assessment. Our staff is available to answer all inquiries pertaining to such notices.

Publication and Inspection of the Tentative Assessment Roll

The Tentative Assessment Roll will be finalized on or before May 1, 2023, and will be available for inspection on this website. An individual property search is also available to check the assessment of a specific property. Inspection of the Tentative Assessment Roll will be available in the Assessor’s Office located at 40 Nassau Avenue as follows:
  • May 1–May 12, 2023 — 8:30 A.M.-5:00 P.M. (Monday–Friday)
  • May 13, 2023 — 9:00 A.M.-1:00 P.M.
  • May 15, 2023 — 8:30 A.M.-8:00 P.M.
  • May 16, 2023 — 8:30 A.M.-9:00 P.M.

Filing of Grievance Complaints

Should you wish to challenge your assessment, you may file a Grievance Complaint with the Assessor’s Office as soon as the Tentative Assessment Roll is finalized. Any Grievance Complaint that is not received by the Assessor’s Office by 9:00 p.m. on Grievance Day, Tuesday, May 16, 2023, will be dismissed by the Board of Assessment Review (BAR) as untimely.

If the person or entity filing a Grievance Complaint is a Town of Islip Employee or their family member, please click here for the additional Disclosure Form that is required pursuant to Chapter 14 of the Islip Town Code.

Hand deliver your Grievance Complaint to Suite 3 of the Assessor's Office located at 40 Nassau Avenue, Islip, New York. Please see Publication and Inspection of the Tentative Assessment Roll above for dates, times, and requirements.

Grievance Day Hearings

On Grievance Day, May 16, 2023, the Board of Assessment Review (BAR) will meet to hear any complaints in the Office of Economic Development Conference Room at 40 Nassau Avenue, New York. All Grievance Complaints will be reviewed in detail by the BAR — appearance by the taxpayer is not required to file a Grievance Complaint or to have it reviewed. All taxpayers who wish to be heard on their Grievance Complaint may appear in person during the following times:
  • 9:00 a.m. to 11:00 a.m.
  • 2:00 p.m. to 4:00 p.m.
  • 7:00 p.m. to 9:00 p.m.
If you wish to be heard on your Grievance Complaint in person, you must sign-in with your full name, Complaint No. (obtained from the Assessor’s Office when you filed your Grievance Complaint), physical property address, and contact information.

Board of Assessment Review Determinations

On or about July 1, 2023, the BAR will issue determination letters for all Grievance Complaints. All determinations will be sent via regular mail.

General Information

Informal Assessment Review

Please keep in mind, not only is our staff available to answer your assessment and exemption inquiries, our office is available for informal assessment reviews prior to March 1st of any tax year, well in advance of Grievance Day. The Assessor must value real property as of July 1st of the year prior to Grievance Day. The Assessor must also value the real property in its condition and use as of March 1st immediately prior to Grievance Day. Upon written request, if the property owner wishes to share sufficient proof of the market value of their property, our office will consider such proof prior to setting the tentative assessment for the property for the upcoming tax year. For example, an appraisal prepared for refinancing purposes and a valuation date within one year of the July 1st valuation date may be useful in a request for an informal assessment review. Likewise, an "arm's-length" sale of the subject property close to the July 1st valuation date may suggest a lower assessment.

Assessment Estimates

Upon written request, our office also provides property owners with assessment estimates, in advance of a property owner adding inventory to their real property (e.g., adding an in-ground pool, a bathroom or an addition). Such assessment estimate request forms are available for residential and commercial properties. The assessment estimate is good for one year, and is valid for the improvements contained in the assessment estimate form.

We look forward to assisting you.

Visit the Assessor's Office homepage at for more information.

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