The 21-year-old gets picked up by cops in Chicago!

ET has confirmed that 'Transformers' star SHIA LABEOUF was arrested over the weekend in Chicago after refusing to leave a Walgreens store.

Police tell us that at about 2 a.m. Sunday Shia repeatedly refused to exit a Walgreens, leading a security guard to detain him until police arrived. He was arrested and booked on a misdemeanor charge of "criminal trespassing."

Cops say the 'Disturbia' star was "very courteous and polite" during booking. He posted a bond and was released before 7 a.m.