Dykstra filed the suit seeking unspecified damages against the county and several Sheriff's Department employees, saying his head was slammed against the wall, his teeth were knocked out and he was kicked and beaten until he was "barely breathing."
The suit says the jail system, where a federal probe has led to 20 recent indictments of sheriff's employees, is "fueled by abusive violence, and manipulated by hopeless liars."
The lawsuit also alleges that top officials at the jail tried to keep Dykstra from speaking out about the incident.
Dykstra had a 12-year career with the New York Mets and Philadelphia Phillies from 1985 through 1996 and spent years as a businessman before running into a series of legal woes several years ago.
The alleged beating occurred in April 2012, the same month Dykstra pleaded no contest to exposing himself to women he met on Craigslist. He was already serving time for grand theft auto and providing a false financial statement, and would later be sentenced to six months for bankruptcy fraud. He was released last June.
The Sheriff's Department had no immediate comment on the lawsuit, which was first reported by the website TMZ.
But when the beating allegations arose at Dykstra's fraud sentencing in December 2012, sheriff's spokesman Steve Whitmore said there had been a fight involving the former ballplayer and some deputies in April. Dykstra was the aggressor and had to be physically restrained, Whitmore said.