Situated in Oakdale and named Indian Neck Hall, it was home of Frederick G. Bourne, president of the Singer Sewing Machine Company. It was completed in 1899 and sat on 438 acres (much of which has since been sold off). Six years after Bourne died in 1920, the mansion became the site of LaSalle Military Academy operated by the Christian Brothers, a catholic order. In 1993, the brothers converted the academy into a kindergarten-through-high school "global learning community". Today part of it is used by the St. John's University School of Graduate Studies.
There are also catering events held in the main part of the mansion.
See http://www.newsday.com/long-island/suffolk/st-john-s-40m-plan-to-save-bourne-estate-1.3009259 for the latest on the mansion.