The Rams brought in six new faces over the summer, while allowing five players to leave Pride Park.
"The transfer window, on the whole, was a good one for us," he told Derby's official website.
"We're pleased with the players we've brought in since the end of last season. We've strengthened in the areas we wanted to and we feel happy with the look and feel of the squad.
"When the players reported back for pre-season training in June and July, we said the squad was the strongest we've had for some time, and that's how we feel."
Derby currently sit 14th in the Championship table.