Dawkins joins Steve McClaren's men for an undisclosed fee, believed to be worth in the region of #500,000, on a two-and-a-half year contract.
The 26-year-old attacking midfielder joined the Rams from Spurs on a three-month deal in October and has scored three goals in his 13 appearances.
''Simon has done really well whilst on loan with us and he's made himself a regular fixture in our attacking line-up,'' said Derby head coach McClaren.
''He's a player we like and I think he brings a lot to the team; he can create goals and, as we've seen, he can score them himself.
''During his three months with us Simon has proved his worth and we're delighted he's agreed to join us on a permanent basis.
''We think he'll only improve as he continues to play games and after just turning 26 we think his best years remain ahead of him.''
Dawkins' contract at Tottenham was due to expire in the summer, although the Barclays Premier League club had an option to extend the deal by a further 12 months.
Derby are moving early in the transfer window with the Dawkins signing coming hot on the heels of extended loan deals for Michael Keane and Zak Whitbread.
Manchester United centre-half Keane will be with the Rams until the end of this month and is eligible to play in Sunday's FA Cup third-round tie against Chelsea at the iPro Stadium. He has started the last three league games in place of injured skipper Richard Keogh.
Whitbread's loan from east midlands rivals Leicester will now run until the end of the season.
Meanwhile, Chelsea striker Patrick Bamford will join Derby next week on loan for the remainder of the season.
The 20-year-old will link up with the Rams on Monday when his current loan spell at League One side MK Dons ends this weekend.
- Sports & Recreation