Probation began in Boston in 1841, when a bootmaker took charge of drunks who otherwise would have heard the cell door close behind them. John Augustus put all the elements of probation into place, from intake to investigation to supervision, becoming the world's first probation officer.
New York State started up probation in 1893, as the practice rolled out in state after state following the example of Massachusetts. The New York City service reported to the judiciary until it was transferred to the executive branch in 1974, with the birth of the city agency.
DOP followed the traditional rehabilitative approach until the explosion of crime beginning in 1968-72 eventually led to both mass incarceration and mass probation, and probation across the country became punitive in nature.