Mill is fighting for release while appealing a two- to four-year sentence for a probation violation.
Mayor Kenney spoke to the Philadelphia-born rapper for an hour.
"I think nationwide we need to look at how we handle criminal justice issues and how we treat people when they're younger and shouldn't follow them when they're older. They have responsibilities to take care of children, child in this case, and be better off doing that if he went to work," Kenney said.
New England Patriots owner Robert Kraft and Philadelphia 76ers co-owner Michael Rubin also visited Mill on Tuesday.
Judge Genece Brinkley said Mill's drug use, arrests and other issues while under supervision merited the jail time.
Mill's lawyers claims the sentence was part of a "personal vendetta."
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