New figures show 59% of the country favourably rate the Holy Father compared to an all-time high of 76% at the start of 2014.
The current rating is similar to when Francis was first elected to lead the Catholic Church in March 2013.
His popularity swelled between then and February 2014 in America as he tried to steer the Church to be more focused on the poor and increased respect for gay and lesbian members.
Despite being named Time magazine's Person of the Year in 2013 his support has not held up.
In the latest poll, conducted for the website Gallup, there's been a 27% drop in support from conservative Catholics,
The website says this drop could be attributed to Francis' denouncing of "the idolatry of money" and his calls for action on climate change.
Its figures also show that one-quarter of Americans have never heard of him or have no opinion - an increase of 16% in 2014.
Pope Francis will visit the United States in September, travelling to New York, Philadelphia and Washington, D.C. before being the first pontiff to address US Congress.