Costello, 58, of Riverhead, is running on the Democratic, Green, Working Families and Women's Equality lines. She has been a private practice attorney since 1986, concentrating in matrimonial and family law, wills and estates, real estate and criminal law. From 1981 to 1985, Costello worked for the New York City corporation counsel's office in the family court unit and later in the special litigation unit and medical malpractice unit. She received a bachelor of science degree from St. Francis College in 1978 followed by a law degree from St. John's University School of Law in 1981. She was admitted to the New York State bar as well as the U.S. District Court for the Eastern and Southern districts in 1982. She is a member of the Suffolk County bar association (family law and trust and estates sections), Suffolk County Matrimonial bar association, New York State bar association and Suffolk County Women's bar association. She also was part of the Suffolk County Bar Association's Pro Bono Project, which has awarded her Pro Bono Attorney of the Month three times, most recently in November 2014. For 10 years she was a law guardian in Suffolk County Family Court, as well as assigned counsel in the East End justice courts. She also has been appointed as a small claims arbitrator in the Suffolk County courts. Costello serves on the Town of Riverhead Board of Ethics and is the treasurer of the Riverhead Community Awareness Program.