Who was put in jail for sitting in the whites only car in Louisiana

Homer Plessy

Explanation:

He sat in the "whites-only" passenger car. When the conductor came to collect his ticket, Plessy told him that he was 7/8 white and that he refused to sit in the "blacks-only" car. Plessy was immediately arrested by Detective Chris C. Cain, put into the Orleans Parish jail, and released the next day on a $500 bond.