The White House has been trying to ensure a high number of attendees in the face of potentially poor weather and a free concert at the far end of the National Mall from the Lincoln Memorial, the Washington Post reported.
Crowd size has been a sore point for Mr Trump, who has repeatedly claimed in the face of the evidence that attendance at his inauguration was the highest ever.
The president is set to speak in front of a ticket-only crowd of Republican donors, administration and campaign officials, family members and those who gather to either hear him or protest his policies.
It has been nearly seven decades since a president spoke on the Mall on independence day. The Korean War was taking place when Harry Truman addressed a large gathering on the Washington Monument grounds to mark the 175th anniversary of the signing of the Declaration of Independence.
Mr Trump is expected to be flanked by military vehicles amid a huge mobilisation and plans for fly-pasts by fighter jets and a stealth bomber.
He dismissed complaints at the probable high cost of the extravaganza in a tweet on Wednesday.
“The cost of our great Salute to America tomorrow will be very little compared to what it is worth. We own the planes, we have the pilots, the airport is right next door (Andrews), all we need is the fuel. We own the tanks and all. Fireworks are donated by two of the greats. Nice!” he said.
The cost of flying a B-2 Spirit stealth bomber for one hour is $122,311 (£96,500), according to the US Air Force.