In one of the largest police-brutality settlements in Long Island history, Suffolk County officials will cough up $2.5 million to the wife and young son of a mentally ill Lindenhurst man who died after a struggle with cops in 2011, court papers state.

Daniel McDonnell, 40, was arrested for violating an order of protection and became unruly after being denied medication at a West Babylon precinct.

A state Commission on Correction report found that McDonnell — who was beaten and Tasered by Suffolk County cops — was the victim of a homicide and that local officials failed to properly investigate the death.

The carpenter suffered from acute bi-polar disorder.

Suffolk County attorneys scrapped their defense on the second day of a civil trial in Brooklyn federal court in May and agreed to settle the lawsuit.

The amount was approved by Judge William Kuntz on Thursday after getting signed off on by the Suffolk County Legislature.