At about 10 p.m., Andrea Roberts was found unresponsive in her assigned cell during routine cell checks.
The jail supervisor who found her "immediately began to render aid and resuscitation efforts," according to the La Porte County Sheriff's Office.
Roberts -- a mother of two -- was taken to La Porte Hospital, where she was pronounced dead.
Roberts had been at the La Porte County Jail since June 2. She was being held on several warrants that included both misdemeanor and felony charges, officials said.
An autopsy is scheduled for Monday. The La Porte County Sheriff's Office said they are investigating the death.
On Sunday, her family had many questions. They received a call early Sunday, but got few answers and suspect foul play.
"We're not understanding how one day you're talking to her on the phone and she's perfectly fine, then the next day, you get a phone call at 2 o'clock in the morning saying that she's deceased, but you don't know how," said Sade Williams, Roberts' niece.
Family said Roberts had about two more weeks remaining on her sentence and was not suicidal. She shared the cell with another inmate, who relatives said also suffered a respiratory or cardiac arrest. Authorities have not confirmed the condition of Roberts' cell mate.
"I think something happened and they don't want us to know," said Roberts' aunt Diane Williams.