Governor Josh Shapiro and his family were evacuated from the Pennsylvania Governor's Residence after celebrating Passover when a man allegedly set fire to the building ... and, the suspected arsonist is now in custody.

Cody Balmer -- a 38-year-old man from Harrisburg, PA -- was arrested after cops say he hopped over a fence onto the property and forcibly entered the residence before setting it ablaze.

Photos of the fire damage show the inside of this part of the residence -- a large room meant for holding big gatherings -- burned badly ... with ashes covering the floor and tables while only a stack of plates in the center of one table seemed to have survived.

The windows of the building are shattered ... though it's unclear if this was caused by the fire or by someone breaking through them.

Cops allege Balmer brought a homemade incendiary device onto the property for attack they claim was carefully planned.

Governor Shapiro told reporters that he was woken up at his home by state troopers at around 2 AM Sunday morning ... who evacuated himself, his wife, their four children, their two dogs and another family that celebrated Passover -- a Jewish holiday commemorating the Israelites exodus from slavery -- with them Saturday night.

Dauphin County District Attorney Francis Chardo has already announced Balmer will be charged with attempted murder, terrorism, attempted arson and aggravated assault though that hasn't been made official yet.

While the motivation for the attack is unclear, Governor Shapiro has seemingly indicated that he believes this was done because he is Jewish ... saying, "When we were in the state dining room last night, we told the story of Passover. I refuse to be trapped by the bondage that someone attempted to put on me by attacking us as they did last night.”

The room where where they celebrated Passover was the room that was burned.