Yes it's free.... I was just there and got some and they loaded me up with a front end loader full of mulch...
There is free mulch available check this link below to see the types at each station. https://www.fairfaxcounty.gov/publicworks/recycling-trash/mulch-message
I dont think its free, they do have mulch dispenser you can drive up to. Looked at their website here is the link https://www.fairfaxcounty.gov/publicworks/recycling-trash/free-mulch
Thanks! Your answer is awaiting moderation.