Openers put Leicestershire in great position against Derbyshire
After Derbyshire’s last two wickets had fallen for just one run in 11 balls, Horton and Dearden added 97 to put the visitors 183 in front at lunch with 65 overs left in the day.
Derbyshire resumed 87 behind on first innings at 532 for 8 but Clint McKay struck with the third ball of the morning by having Rob Hemmings caught behind and Tony Palladino then gloved a pull to give Zak Chappell his fourth wicket.
Horton, who was dropped on eight at first slip off Tom Taylor, was 46 at lunch with Dearden unbeaten on 48.