My landlord of 4 yrs illegally evicted me. now is suing me in Civil Court for back rent, can i sue for illegal eviction,

In the State of New York, the landlord can NEVER use self help to remove you from your apartment. Only a Marshal can remove you and only after the Marshal gets an Order from the Court. It would take a few months for the landlord to go through the legal process to remove you. If the landlord changed your locks within 7 days, this is most certainly an illegal eviction.

My response would go to Court, get a finding of illegal eviction and then commence an action in Civil Court for treble damages as a result of the illegal eviction.

In such a situation, I would have brought an Order to Show Cause and had you restored to possession within a few days of the illegal eviction.

Your legal recourse is very strong but you must take action against your landlord to prove you were illegally evicted and preserve your rights against the landlord.