Trump hits 100 days on April 29 next Saturday.
He tweeted about the rally today, saying that next week "I will be holding a BIG rally in Pennsylvania. Look forward to it!"
April 29 is also the annual White House Correspondents' Association dinner in Washington.
Most presidents attend the event. Trump previously announced that he is boycotting this year's dinner to protest what he says is unfavorable coverage by the news media. His staff is also boycotting in a show of "solidarity" with the president.