Why is Eid-ul-Fitr determined to be Monday, June 26th? The Ahmadiyya Muslim Community uses the calculation of the moon to determine when the moon can possibly be visible by the naked eye. Muslims are not supposed to blindly follow Saudi Arabia. Rather, they are to determine Eid based on when the moon is visible with the naked eye. 
The below image illustrates the different gradients of visibility of the moon on Saturday June 24th (today): 
As you can see, there is no place in the U.S. that is covered in red - meaning that there is nowhere in the U.S. where there is even a possibility that the moon will be visible today with the naked eye. There is a small segment of the U.S. that is covered in the orange color, which means the possibility of viewing the moon with the naked eye only in perfect conditions. That is only covering some parts of Southern Cali, Arizona and Southern Texas.
Now look at the map for June 25th (tomorrow): 

As you will see, the entire country (and entire world) is covered with red - meaning that tomorrow we will all be able to see the moon with the naked eye, InshaAllah. We are in touch with the chapters of the Ahmadiyya Muslim Communtiy in the small sliver of the country that can possibly see the moon under perfect weather conditions. If we receive verified reports from any of them, we will post that immediately. Otherwise, we will only be able to see the moon with the naked eye tomorrow. That means Eid is Monday, InshaAllah.