New Jersey is the only state in the country that doesn't issue a child support termination order on the July 1 following the child's 18th birthday (assuming he/she is a high school student until then).
YOU must get an order emancipating the child. If you don't pay after emancipation, eventually the court will contact you. If there's a garnishment for support, it will remain in place until the court orders it to stop.
The good news for you is that, unless the child is continuing on to full time college (or is disabled), child support will cease when she/he turns 18 and graduates from high school. Any support paid after emancipation must be refunded.
PLEASE NOTE THAT AVVO'S "ATTORNEY RANKING SYSTEM" IS NOT RELIABLE. IT IS APPARENTLY EITHER RANDOM OR BASED SOLELY ON YEARS IN PRACTICE (WITH 25+ YEARS REQUIRED FOR TOP RATING). THERE ARE ATTORNEYS LISTED AS "SUPERB" WHO ARE MASSIVELY OVER-PRICED SCHOLCKS WHO SUE THEIR OWN CLIENTS OVER BILLS ON A REGULAR BASIS AND ARE REGARDED AS JOKES BY THE COURT - BY CONTRAST, THERE ARE MANY EXCELLENT, COMPETENT, INTELLIGENT AND EXPERIENCED ATTORNEYS ALL ACROSS NJ WHO ARE LISTED AS "GOOD" OR LESS.
As stated by David, there is no automatic termiantion of child support in N when a child turns 18. Support is due until the child has been declared emancipated. Emancipation is a fact-specifica analysis and considers such thing as whether the chld is continuing their education,employed, etc. it is advisable to consult with an attorney to determine your rights.