College student Jennifer Haskell, 22, passed away on Friday morning at an Indianapolis hospital, her uncle Mike Whited confirmed.
Strong winds of up to 60mph caused the stage's metal scaffolding and equipment to plunge into fans awaiting a set from Sugarland last Saturday night. Four people were killed instantly, with a further 40 injured.
Sugarland singer Jennifer Nettles later said that she was "stunned and heartbroken" by the stage collapse.
The country music band have since announced plans to hold a memorial concert in honour of those who died.
The Indiana collapse was one of two festival tragedies within a week. On Thursday, five people were killed and dozens more injured after a stage caved in at Belgium's Pukkelpop festival.
Watch footage of the stage collapse at the Indiana State Fair below (Warning: contains disturbing scenes):