Hornby (pictured) made six appearances for Port Vale this season but had not played since September when joining the Blues initially for a month in December.
He featured in nine Chester games following his arrival at the Swansway Chester Stadium having had his initial spell extended.
The 22-year-old will now remain with the club for the rest of the campaign.
Chester have also signed defender Shaun Hobson on loan from Premier League AFC Bournemouth for the rest of the season.
The 19-year-old central defender started his career in the youth set up at Burnley before making the move to Dorset in the summer of 2016.
He spent the second half of last season on loan at National League South outfit Eastbourne Borough.