Schodack Police Officer Tom Jones was conducting a Stop-DWI enforcement detail when he stopped Cassidy, 63, of Fort Lauderdale, on the Columbia Turnpike near Miller Road around 2 a.m. Wednesday.
Cassidy had a BAC of .10 percent and has been charged with felony DWI and failure to dim headlights. He was arraigned in the town of Schodack Justice Court and taken to Rensselaer County Jail where he posted $2,500 bail Wednesday morning.
The Chief of Police Bernhard Peter says Officer Jones was too young to know who Cassidy is. He says Cassidy was driving a rental car, visiting friends with his fiancee, and his fiancee wasn't drunk, so she drove away with the car after his arrest.
The police chief says Cassidy "cooperated and was a gentleman."
Cassidy is best known for his role as the character of Keith Partridge in the 1970's musical/sitcom "The Partridge Family." He is known for frequenting the Saratoga Race Course each summer.
Cassidy was previously arrested for DUI in Florida in 2010, making this recent arrest a felony charge.
He is scheduled to return to town court in September.
Police Lt. Joseph Belardo says Cassidy was stopped shortly after 12 a.m. Wednesday about 10 miles south of Albany.
Cassidy's publicist had no immediate comment.
The Associated Press contributed to this report.