Corpus Christi police arrested the boy's mother on a charge of injury to a child after the death Wednesday.
Nueces County Jail records Thursday indicated 26-year-old Concepcion Rodriguez was free on $25,000 bond. Jail officials had no information on an attorney for her.
Police say Rodriguez had her four children and three others in the SUV when she drove to a store and returned home around 1 p.m. Wednesday. The toddler's father arrived nearly three hours later and asked about his son.
The boy was found unresponsive in the vehicle and died at a hospital. Further details on the youngster weren't immediately released.
Temperatures reached the upper 90s Wednesday in Corpus Christi.