Centre-half Pennington, who turned 27 this week, moved to Shropshire on a permanent basis in the summer after a successful loan spell in the second half of last season.
While speaking of how impressed he has been with the former Everton man this season, Cotterill said Pennington reached out to a former team-mate, Leeds' Luke Ayling – a colleague at Elland Road where he spent the 2017/18 season on loan – for an insight into the manager's relationship with players.
Cotterill took Leeds favourite Ayling from Yeovil to Bristol City in 2014, before the right-back earned his move to West Yorkshire.
"He's a very intelligent boy, Matthew. You don't need to speak to him too many times, he gets pictures, understands things, is very eloquent," Cotterill said.
"He's a real, real honest professional and man.
"I actually think he's got better this year. He said when he came in he wanted to get better.
"He'd spoken to Luke Ayling a little bit about my relationship with Luke Ayling, they spoke about me and him (Pennington) coming here and Luke said whatever he said."
Aside from serving a suspension for a red card in the EFL Cup in August, Pennington has been a regular in Town's backline this term.
The defender, who is set to return to another of his former loan clubs in Ipswich with Salop today, is a vocal part of Shrews' defence and a respected member of the dressing room.
Cotterill believes that his summer centre-half acquisition has improved as a footballer since he first checked in on loan at the back end of last December, prior to the manager's Covid illness.
Pennington, who is part of a Town side still searching for a first clean sheet, called time on 16 years at Everton on his release in the summer.
"Matthew came here and I think he has improved this season from day one (last December). In pre-season, not just the fitness work, but a lot of passing drills that Dave Longwell is very good at – that's Dave's strength – the repetition, receiving on your back foot, all those things, I think that's been really important. I think he's improved no end," the manager added.
"He did a good job for us last season but he's done more than a good job this season, he's been better again."