The category 4 storm turned streets into rivers, knocked out power to 1.8 million people and threatened catastrophic damage further inland after it made landfall on Wednesday.
The hurricane slammed the coast with 150 mph winds and pushed a wall of storm surge accumulated during its slow march over the Gulf of Mexico.
More than 1.8 million Florida homes and businesses were without electricity, according to PowerOutage.us. Nearly every home and business in three counties was without power.
A coastal sheriff’s office reported that it was getting many calls from people trapped in homes after the hurricane’s centre struck near Cayo Costa, a protected barrier island just west of heavily populated Fort Myers.
About 2.5 million people were ordered to evacuate south-west Florida before Ian hit, but by law no one could be forced to flee.
Mark Pritchett stepped outside his home in Venice, some 70 miles south of Tampa, around the time the hurricane churned ashore from the Gulf of Mexico. He called it “terrifying”.
“I literally couldn’t stand against the wind,” Mr Pritchett wrote in a text message. “Rain shooting like needles. My street is a river. Limbs and trees down. And the worst is yet to come.”
News anchors at Fort Myers television station WINK had to abandon their usual desk and continue storm coverage from another location in their newsroom because water was pushing into their building near the Caloosahatchee River.
Though expected to weaken to a tropical storm as it marches inland at about 9 mph, Ian’s hurricane force winds were likely to be felt well into central Florida. Hours after landfall, top sustained winds had dropped to 125 mph, making it a Category 3 hurricane. Still, storm surges as high as 6 feet (2 metres) were expected on the opposite side of the state, in north-east Florida.
“This is going to be a nasty, nasty day, two days,” Florida Governor Ron DeSantis said, urging people in Ian’s path along the Atlantic coast to rush to the safest possible shelter and stay there.
Jackson Boone left his home near the Gulf coast and hunkered down at his law office in Venice with employees and their pets. Mr Boone at one point opened a door to howling wind and rain flying sideways.
“We’re seeing tree damage, horizontal rain, very high wind,” Mr Boone said by phone. “We have a 50-plus-year-old oak tree that has toppled over.”
In Naples, the first floor of a fire station was inundated with about 3 feet (1 metre) of water and firefighters worked to salvage gear from a firetruck stuck outside the garage in even deeper water, a video posted by the Naples Fire Department showed.
Naples is in Collier County, where the sheriff’s department reported on Facebook that it was getting “a significant number of calls of people trapped by water in their homes” and that it would prioritise reaching people “reporting life-threatening medical emergencies in deep water”.
The storm previously tore into Cuba, killing two people and bringing down the country’s electrical grid.
Ian’s strength at landfall tied it for the fifth-strongest hurricane when measured by wind speed to strike the US. Among the other storms was Hurricane Charley, which hit nearly the same spot on Florida’s coast in August 2004, killing 10 people and inflicting 14 billion dollars (£12.9 billion) in damage.
Ian had strengthened rapidly overnight, prompting Fort Myers handyman Tom Hawver to abandon his plan to weather the hurricane at home. He headed across the state to Fort Lauderdale.
“We were going to stay and then just decided when we got up, and they said 155 mph winds,” Mr Hawver said. “We don’t have a generator. I just don’t see the advantage of sitting there in the dark, in a hot house, watching water come in your house.”
Florida residents rushed ahead of landfall to board up homes, stash precious belongings on upper floors and join long lines of cars leaving the shore.