South Africa-born McKerr joined Derbyshire on an initial 28-day loan deal on 31 May.
The 19-year-old took 14 wickets in two first-class games for Derbyshire.
He also became the youngest player in the county's history to take 10 wickets in a match when he took 10-141 in their defeat by Northamptonshire.
Meanwhile, Derbyshire opening batsman Luis Reece is still hopeful of being fit from a viral infection for the county's next game, the inaugural day-night Championship game against Glamorgan, in Cardiff, starting on 26 June.
Reece, 26, did not bat in either innings in Derbyshire's three-day defeat by Northamptonshire at Wantage Road on Sunday, after leaving the pitch on Friday with breathing problems.
"I was struggling to breathe," the winter signing from Lancashire  told BBC Radio Derby. "Then, a couple of overs later, I felt tightening in my chest, the paramedics were on and I was off to Kettering Hospital.
"They think it's a viral infection and it was fluid that caused the tightening of the chest. I can't do any strenuous exercise and I'm being referred to a cardiologist.
"But hopefully I will be available for the next game. I'm hoping that it's not going to be a long lay-off. And I'll know more once I've seen the cardiologist."

United manager Jose Mourinho is keen on the 22-year-old, who can play at centre-half or right-back.
A group from Benfica is reported to have travelled to England on Monday to discuss a potential transfer with the Premier League club.
United have not commented but Vitoria said: "If there are exits we will find solutions."
Reports suggest he would become the club's most expensive defender of all time, costing between £38m and £42m. Their record is England international Rio Ferdinand's £29.1m move to Old Trafford from Leeds in 2002.
Lindelof, who has 11 caps for Sweden, played in Benfica's Portuguese league game against Rio Ave on Wednesday, their last game for two weeks.
His agent Hasan Cetinkaya told Swedish media there was "a bid on Benfica's table" and that he would be meeting with the club, but refused to comment when asked specifically about an offer from Manchester United.
Mourinho, who spent more than £150m on players in the summer, is keen to make changes to his squad during the January transfer window.
Although the Portuguese has said he will not force anyone out, midfielders Morgan Schneiderlin and Bastian Schweinsteiger are the most likely to depart, along with Memphis Depay.
France international Schneiderlin, 27, has attracted interest from Everton, as has Netherlands winger Depay, although Italian side Roma are another club keeping an eye on the 22-year-old.
Former Germany captain Schweinsteiger spoke to MLS outfit Chicago Fire, with other US clubs also keen on taking the World Cup winner, who has returned to first-team training after being frozen out by Mourinho at the start of the season.
Surrey have recalled paceman Conor McKerr from his loan spell with County Championship Division Two side Derbyshire, with immediate effect.
[NEXT_CONCEPT]
Benfica coach Rui Vitoria has not ruled out Sweden defender Victor Lindelof joining Manchester United next month.