Kevin Strickland was freed on Tuesday at the age of 62. He had maintained his innocence since his arrest at 18.
It was the longest wrongful incarceration in state history, but under Missouri law he is not entitled to receive any financial compensation.
So his lawyers launched a GoFundMe page to help with his living expenses.
As of Sunday 16:00 GMT, it had reached $1,511,440.
Lawyers for the Midwest Innocence Project, who worked for months to help free Mr Strickland, praised the more than 27,000 strangers who had donated.