Firefighters said they took Cronin to Ocala Regional Medical Center, where she later died.
Firefighters returned to Walmart after receiving multiple calls from people who were suffering distress from the shooting, officials said. Firefighters treated two people at the scene and took another person, who had been injured while people were evacuating the store during the shooting, to a hospital, officials said.
Authorities tracked Johnson to the house he and Cronin shared on NE 35th Street, officers said.
Johnson shot himself before police apprehended him, according to authorities. He was taken to a hospital for treatment.
Johnson has served multiple prison sentences since 1987 for convictions on charges including burglary, carjacking and drug-related crimes in Marion County, records from the Florida Department of Corrections show. He was most recently released from prison at the end of 2013.