Typically most major retailers in the United States open on the Friday after Thanksgiving Day for their Black Friday sales. By Friday is one of the busiest shopping days of the year and over the last few years some companies have begin opening even earlier. It's common for some retailers to open at midnight on the Friday after Thanksgiving.
Some retailers have been announcing that they'll be opening on Thanksgiving day to allow shoppers to begin shopping even earlier. One of the stores that has announced it would be opening on Thursday, November 28 at 8 PM was Macy's. JC Penney has now announced that it will follow suit.
JC Penney will be opening at 8 PM on Thanksgiving day. The retailer says that most of its 1100 locations will be open at 8 PM on Thanksgiving Day. That leaves the door open for some locations to remain closed. You need to check with your local store to see if you'll be able to start shopping on Thanksgiving Day.