Go through your results for flights to Rockford in USA with Netflights.
Flexible on dates? Conducting your search by month allows you to compare prices to Rockford throughout the year. Accommodation prices will also be higher at this time of year.
So, if the flights to Rockford don't work for you, you could always try searching for flights to other airports in USA.
Looking at a few different departure airports will give you even more choice. See what you can find. And remember, it's best to book your flights in advance wherever possible.