From the United States’ Bishops website:
Pope Francis made his intention to travel to the United States for the 2015 World Meeting of Families. . . public on November 17, 2014, in an address to the Colloquium on the Complementarity of Man and Woman at the Vatican.
Archbishop Joseph E. Kurtz, president of the United States Conference of Catholic Bishops welcomed the news.
“The presence of Pope Francis at the World Meeting of Families in our country will be a joyful moment for millions of Catholics and people of good will. Our great hope has been that the Holy Father would visit us next year to inspire our families in their mission of love. It is a blessing to hear the pope himself announce the much anticipated news,” said Archbishop Kurtz.
The schedule for the pope’s visit to the three US cities is here.