The intruder, Elizabeth Pahlke, was arrested at about 5:30 p.m. Tuesday. She is being held on $150,000 bail. She faces charges of felony stalking and burglary.
Authorities say she first tried to break in through a window, but she was caught scaling a fence on the ground.
Cusack's security detained her until sheriff's officials arrived.
According to sources, the actor was not at home at the time of the incident.