The Islip Town Board holds a public hearing on the Heartland Town Square development on Wednesday — one of the last steps before board members vote on whether to grant approval to the massive development in Brentwood.

Developer Jerry Wolkoff has been trying to launch the mixed-use development at the former Pilgrim State Hospital site for the past 15 years. He is seeking a zone change for the site off the Sagtikos Parkway from residential to a newly established Pilgrim State Planned Redevelopment District.

Wolkoff purchased the 450-acre plot from the state in 2002 for $20 million and originally intended to build a mixed-use development that included 9,000 apartments, 3 million square feet of office space and 1 million square feet of retail.

The Islip Planning Board last year granted approval for a modified version of the plan, with an initial construction phase monitored by the town for potential traffic and infrastructure impact. The first phase of construction is to take place on a 133-acre portion of the site. The height of buildings in the first phase is limited to five floors, which reduced the original proposal’s overall square footage by nearly 1.9 million square feet.

In February, the Suffolk County Planning Commission unanimously voted to recommend that the Islip Town Board grant the zoning change.

Some local leaders have publicly stated their support, including John Jay LaValle, chairman of the Suffolk County Republican Committee, who sent out an email Monday asking for supporters to attend Islip’s public hearing.

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“The project will immediately catalyze thousands of construction jobs and its economic boost is expected to create 25,000 permanent jobs overall,” LaValle wrote in the email.

Mitch Pally, chief executive officer of the Long Island Builders Institute, said he plans to testify in favor of the project.

Richard Amper, executive director of the Long Island Pine Barrens Society, and Brentwood school board member Roberto Feliciano have opposed the project over its potential impact on the environment and school enrollment.

The hearing starts at 6 p.m. at Town Hall West at 401 Main St. in Islip. For more information about the proposed development, visit islipny.gov/heartland.

Town officials are asking residents who want to comment to arrive at the hearing early to register, starting at 5 p.m. No props or backpacks will be allowed inside the building, officials said.