Was Pope Gregory IX a saint?

Non-Catholic point of view
The Bible clearly teaches that ALL Christians are saints. This can be clearly found in the writings of the Apostle Paul int he books of Romans, Corinthians, Galatians, Ephesians ect. The idea that only a select few who are chosen to be saints by religious leaders or politicians is a heresy not taught in the bible.

True Catholic point of view
The Catholic Church also recognizes that all followers of Christ, living or dead, who are in a state of grace in His eyes are also saints. A mass murderer or rapist may believe in Christ but would hardly be classified as a saint. However, the Church also chooses to honor a few of these holy ones with the title of saint. They have been thoroughly investigated and found to be worthy of emulation by the faithful still on earth. In other words, they are good role models. From the earliest days of the Church, for nearly 2000 years, these exemplary Christians have been so honored. All in heaven are saints but only a few make good role models for the living. There is nothing heretical about this. However, to deny this Communion of Saints is heretical. When we honor the saints, we honor their Creator.

To now answer your question, Pope Gregory IX was quite a controversial pope and is not considered as a named saint. Considering some of the things he did as pope, he is definitely not one that would be considered as a role model. This does not mean he may not be a saint. He very well could be. Only God can make that decision based on the condition of his soul when he died.