The plane belonged to Puerto Rico Air National Guard and was on a training flight, the National Guard said.
The nine dead servicemen were identified as having ranks ranging from senior airman to major.
In July past year 16 service members were killed in a KC-130 crash in Mississippi.
The mayor of Manati, along Puerto Rico's north coast, said Maj.
Puerto Rican authorities say there were nine people aboard the cargo plane that crashed outside the Savannah, Georgia, airport.
Capt. Jeff Bezore of the Georgia Air National Guard's 165th Air Wing said he couldn't say how many people in total were on the plane that crashed Wednesday around 11:30 a.m.
President Trump tweeted that he had been briefed on the crash, and sent "thoughts and prayers for the victims, their families and the great men and women of the National Guard".
The investigation is being carried out by the National Guard Bureau and the Air Force, Rivera said.
The most recent accident before Wednesday's deadly crash in Georgia happened July 10 when a Marine Corps KC130T transport plane crashed in MS, killing 15 Marines and a Navy sailor when it slammed into a soybean field near Itta Bena.
"The planes that we have in Puerto Rico - it's not news today that they are the oldest planes on inventory", Rivera said.
Dahlen said the aircraft had undergone routine maintenance just before leaving Savannah.
The aging plane had rescued and resupplied American citizens after last year's hurricanes as part of the US territory's fleet, which often struggles to remain mission-ready amid long waits for spare parts, said Adjutant Gen. Isabelo Rivera, commander of the Puerto Rico National Guard.
The site of a military plane crash is seen in Savannah, Georgia.
All nine people on board an aging USA cargo plane have been killed when the aircraft making its final military flight nose-dived into a highway in the U.S. state of Georgia, an official said.
"The town is in mourning", Sanchez said. Jose Rafael Roman was the pilot.
Boone also said he was unsure if the plane was flying to Arizona to be decommissioned, despite reports to that effect.
Adjutant General Isabelo Rivera says the aging C-130 Hercules had been used to rescue and resupply US citizens after last year's hurricanes, among many other missions.
When it crashed, the plane was en route to Arizona into retirement, reducing the Puerto Rican Guard fleet to five similar planes, two of which need maintenance and aren't being used, Rivera told reporters, according to the Associated Press.
Nine Puerto Ricans were on board Wednesday for what was supposed to be its final flight before being retired in Arizona. The plane hit the ground so hard that the only intact part of the aircraft was the tail section.
However, Spencer said that the increase in what the military characterizes as "Class C mishaps" - accidents that cause between $50,000 and $500,000 in damage to aircraft without loss of life - could be a "leading indicator" of potentially more serious problems ahead.