The 34-year-old midfielder reached the landmark in the Tigers' 1-1 draw at Reading, having made his competitive debut for Derby on the final day of the 1994/95 season.
Speaking to the club's official website, Ashbee said: "From the age of 30 it was a landmark I wanted to achieve.
"It's a big thing for me and I think 500 is a good innings at any level of the professional game.
"To reach that figure considering I had two long-term injuries that ruled me out for two-and-a-half seasons in total is a fantastic achievement.
"I can definitely feel all 500 games in my legs and body though - that's for sure."