Two of the fires were set at houses on the same street -- 609 and 1011 Vermont Street. The third fire was set at 506 Rosewood Drive.
Investigators say the fires started early in the morning in vacant houses that are for sale. The fires are similar in the way they were set.
Police say it is too early to speculate about suspects or motives. They are asking residents in the area to be vigilant, watch vacant properties near them and call the police if they notice anything suspicious.
Anyone with information about the fires can contact the Smithfield Police Department 919-934-2121 and ask to speak with Lt. Powell or Detective Johnson. A reward is being offered for any information that leads to an arrest in connection with these cases.