The Orange County jury made the unanimous finding Thursday after less than an hour of deliberations.
Sheryl Lynn Massip had asked jurors to declare her legally sane so she would no longer have to get mental health treatment or home visits. She claims postpartum psychosis led her to kill her 6-week old son, Michael, in 1987.
A jury convicted Massip of murder in 1988, but a judge set aside the verdict and found her not guilty by reason of insanity. She has never served time in prison or a state mental hospital.
Massip is remarried and has a daughter.