The 23-year-old midfielder was signed a year ago after being released by Hull City, but an ankle injury restricted him to only 13 league starts last term.
"It's been a frustrating few months with the injury but I am 100% fit now," he told Crawley's website.
"It [the contract] gives me the opportunity to hit the ground running in pre-season and hopefully impress the manager enough to get another one."
Henderson, who began his career at Arsenal, played only one first-team game during his year at Hull and was loaned out to Stevenage.
"This is a fresh start for Conor," said Crawley manager Mark Yates.
"I know he has a lot of ability and he has the chance now to show what he's about."

Kim Wall, 30, was last seen on Thursday evening on board the vessel with the owner, 46-year-old Peter Madsen.
The submarine later sank and Mr Madsen was rescued before being arrested and charged with manslaughter.
The stricken vessel, the Nautilus, has been raised but no body was found and the search for Ms Wall goes on.
Mr Madsen initially said that he dropped Ms Wall off before it sank but police say he has now changed his statement - although they have not said what to.
Police gave no other information on why they thought the Nautilus was deliberately sunk, but it contradicts Mr Madsen's explanation that there was a technical fault.
Mr Madsen has denied involvement in Ms Wall's death, and will be held in custody for 24 days while investigations continue.
Ms Wall's boyfriend first reported her missing after she failed to return from what should have been a short trip on the submarine.
She had been writing about Mr Madsen and his submarine, which at one stage was the largest privately-made vessel of its kind.
Police are still appealing for witnesses who may have seen Ms Wall on Thursday evening.
"We're still hoping that we'll find Kim Wall alive, but we are preparing  ourselves for the fact that she may not be," Copenhagen police homicide chief Jens Moller said.
Conor Henderson has agreed a new six-month contract with Crawley Town.
[NEXT_CONCEPT]
Danish police believe that a submarine at the centre of an investigation into a missing Swedish journalist was deliberately sunk.