About MMKO

MMKO has a long and successful history of guiding our clients through the obstacles and responsibilities of administering an estate or trust. In 2008, John P. Mahon celebrates 60 years of service as a lawyer to his clients, handling numerous estates and trusts over those years. In addition, Richard T. Kerins served as the Nassau County Public Administrator and Deputy Public Administrator from 1987 to 2001, during which time he administered thousands of estates. During that same time, Lawrence Mahon and Kenneth P. Mahon served as counsel to the Public Administrator.

"Almost right is wrong!" is the motto greeting our clients in our lobby. It's a daily reminder of our commitment to provide exacting care and personal attention to our clients' needs. We provide help with estate administration, personal injury, employment and elder law, estate and trust litigation, estate planning, wills and trusts, wrongful death cases, business transactions, powers of attorneys, insurance trusts, family limited partnerships, asset protection trusts, dynasty trusts and more.


JOHN P. MAHON is the founder of Mahon, Mahon, Kerins & O’Brien, LLC and is now Of Counsel to the firm. On November 22, © 2020, Mr. Mahon celebrated 65 years admission to the New York State Bar.

Mr. Mahon attended St. Francis College until he entered Military Service in 1942. After his Honorable Discharge from the Army Air Corp/U.S. Air Force in 1945, Mr. Mahon attended St. John's University. In 1948, he obtained his J.D. from St. John's University School of Law where he was a member of the Law Review. He then obtained his LL.M in Labor Law and Aviation Law from New York University in 1952.

Mr. Mahon is a member of the American Bar Association, New York State Bar Association, Nassau County Bar Association and a Charter Member of the Catholic Lawyers Guild. He has been a frequent lecturer and active member of the Nassau County Bar Association, the New York State Bar Association, American Bar Association, Catholic Lawyers and many Elder Law Community Service Groups including:

  • Director, Nassau County Bar Association
  • Former Bar Association Chairman
  • Community Relations
  • Tel-Law
  • General Practice
  • Consumer Affairs
  • Health Advocacy
  • Lawyer Referral
  • Library Lecture Series
  • Bicentennial Celebration
  • Former Member, Citizen's Education Committee (State)
  • Representative of Bar Association
  • Channel 4 Community Advisory
  • Former Member, Channel 21 Community Advisory Board
  • Former Member Drug Advisory Committee (Wantagh Schools)
  • Former Chairman, St. Frances School Committee
  • Producer & Host of Weekly Radio Show, "Learning about the Law"
  • For over 20 years on WRHU-FM
  • Producer and Host of Weekly Radio Show, "Long Island Community Spotlight"
  • For over 10 years on WRHU-FM
  • Produced Special Issue of New York Law Journal in Celebration of 25th Anniversary of Nassau County Bar Association
  • Planned & Directed "Living Constitution"
  • Installed in Nassau County Supreme Court Lobby

Serving all of NYC (Queens, Brooklyn, Manhattan, Bronx, Staten Island) and Long Island (Suffolk and Nassau County)