Forward Winnall, 26, becomes manager Gary Rowett’s fifth summer signing following the earlier arrivals of Curtis Davies, Andre Wisdom, Tom Huddlestone and Tom Lawrence.
Like Butterfield, he will be unable to play against his parent club this season.
Butterfield, a 27-year-old midfielder, leaves Derby two years after arriving for a reported B£5million from Huddersfield.
County also loaned Craig Bryson to Cardiff for the season before completing a deal for Birmingham midfielder Maikel Kieftenbeld.
The 27-year-old Kieftenbeld will link up again with Derby boss Gary Rowett, with whom he worked at Blues, after signing a two-year deal for an undisclosed fee.