CHICAGO  People awaiting trial here at the Cook County Jail, one of the nation’s largest local jails, have endured vastly inadequate medical care, beatings at the hands of jail workers and dilapidated, dangerous building conditions often left unrepaired for months, federal authorities said on Thursday.

Grim images peppered 98 pages of federal findings from a sweeping 17-month investigation about the jail, a West Side complex of buildings, the oldest of which once housed Al Capone, that is now temporary home to about 9,800 men and women.

The investigation by the civil rights division of the United States Department of Justice and the office of Patrick J. Fitzgerald, the United States attorney here, found that the jail had systematically violated the constitutional rights of inmates. The Cook County Sheriff’s Office, which oversees the jail, strongly denied that.

Among dozens of glimpses of life inside the jail, the federal investigators wrote of an inmate who, after exposing himself to a female officer in July 2007, was handcuffed, then hit and kicked by a group of jail officers. Some inmates were not given their mental illness medications for weeks, the investigators said, while others were given such drugs without records of why. In August 2006, an inmate’s leg was amputated after an infection beneath a cast went untreated.