He told the crowd the media did not want “to report the truth” and had their own agenda.
The gathering in Melbourne is similar in style to those Mr Trump held during the election campaign.
It comes off the back of a week in which Mr Trump attacked the media in an aggressive press conference.
His national security adviser Michael Flynn also quit earlier in the week. Mr Trump is to interview candidates for the role on Sunday.
On Saturday, President Trump and his wife Melania were greeted by thousands of supporters at the rally in a state he won in November’s election. Protesters have also promised to line the route to the venue.
It is unusual for a sitting president to hold a rally in the style of those held during election campaigns. One supporter, Gene Huber from West Palm Beach, said the decision to hold a rally was not a concern. “No jitters at all,” he told the AFP news agency. “This is a world leader now who’s taking control.”
Throughout the week, Mr Trump launched attacks on the media while indicating his excitement at facing crowds in Florida again.
On Thursday, he held a 76-minute press conference where he told reporters their level of dishonesty was out of control, citing coverage of his campaign’s alleged contacts with Moscow.
Michael Flynn, Mr Trump’s national security adviser, resigned on Monday after he misled Vice-President Mike Pence about whether he had discussed US sanctions with Russia’s ambassador before his own appointment.
Meanwhile, the New York Times reported earlier this week that members of Mr Trump’s campaign and other Trump associates had repeated contacts with senior Russian intelligence officials in the year before the election.
While in Florida, Mr Trump is staying at his Mar-a-Lago resort for the third weekend in succession. In a tweet, he referred to the property as the “Southern White House”, although the private club is part of Mr Trump’s portfolio and is not government property.
While there, he will interview four candidates for the role of national security adviser, the White House said.