The sheriff's office shared a picture of a body scan, reminding people everyone is screened before entering the facility.
In the scan, the gun can be seen between the man's legs.
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Philip Robinson, 23, was in the process of being booked into the jail on misdemeanor charges.
The firearm, a 9mm Taurus loaded with 13 rounds including one in the chamber, was safely recovered before it could enter the secure facility, the sheriff's office said.
He's now facing additional felony charges.