Some 20 protesters were still at Courthouse Park when the rain moved in around 8 p.m.Thursday night.
Most of them stuck around for much of the night and into this morning. Tents were set up to help the group stay dry.
Earlier in the week, Fresno County issued another eviction notice reminding protesters to leave the area immediately.
Their permit to assemble expired on Nov. 1 and the group decided not to renew it.
Authorities say violators could face a $500 fine or be arrested.
It's unknown when, or if, Sheriff's deputies will move in and enforce the law.