The Democrat was accused of using computers in his Union County legislative office to view, print and duplicate images of underage girls simulating or engaged in sexual acts.
As an assemblyman, Cohen championed bills aimed at fighting child pornography.
Under terms of the plea agreement, prosecutors will seek a 5-year prison term when Cohen is sentenced on July 12. The 59-year-old would also have to register under Megan's law and agreed never to seek public office again
Cohen checked himself into a psychiatric hospital after giving up his Assembly seat in 2008.
Looking gaunt, Cohen acknowledged being on medications but told the judge the drugs did not impair his judgment.
Cohen left court without commenting.
