The Humane Society of Pinellas participates in the TNVR program. You can call during business hours for more information on feral cats and the services, I'm not sure if it's completely free but they definitely have a mission to help sterilize and release feral cats.
The Humane Society partners with programs like Operation Snip and Meow Now for trap and release. You can reach out to those specific organizations for more information. https://www.meownowfl.org/ http://operationsnipfl.org/
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