Wikipedia says Lloyd-Levitan Productions for Seasons 1-3. After that they started using their own production, I found this as a article.
There's been a divorce in the Modern Family: Vulture hears that Steve Levitan and Christopher Lloyd, the creators and showrunners of ABC's hit comedy, have decided to dissolve the four-year old business partnership that led to the creation of the show. Neither man is leaving Family, but Levitan and Lloyd will now manage the series as single parents rather than as a couple. So why the split? Link -> http://www.vulture.com/2010/07/modern_family_steve_levitan.html
Christopher Lloyd uses Picador Productions, and Steve Levitan uses Steve Levitan Productions from Season 3-Present