Labour MP Mrs Cox died when she was shot and stabbed in Birstall, West Yorkshire, on Thursday.
After her death, her friends set up a fundraising page, with proceeds to be divided between causes she had supported.
In a tweet, her husband Brendan said the money would "change lives".
The fund was pushed past the seven-figure mark shortly before 20:30 BST on Monday by a single £6,000 donation. More than 30,000 people have donated so far.
Money raised will support three charities Mr Cox said were close to his wife's heart - the Royal Voluntary Service, Hope not Hate and the White Helmets.
Mrs Cox's friend Tim Dixon, one of those who launched the fund, said: "The scale and speed of the public response to this fund has been overwhelming and deeply gratifying to Jo's family.
"It shows how powerfully Jo's story has moved so many. Jo would be so proud."
Gofundme, which hosts the appeal, said it was the largest UK campaign it had seen, and the third largest globally.
The fundraising milestone came after MPs gathered in the House of Commons on Monday to pay tribute to Mrs Cox as members of her family looked on.
Friends of Mrs Cox have announced plans for a public event in Trafalgar Square in London on Wednesday, on what would have been her 42nd birthday.
Mr Dixon said her husband Brendan was doing "an amazing job, and we're telling him that".
He said: "Over the weekend, he was thinking about how having kids just three and five years old, they're not going to have many memories of their mother when they grow up - he wants to capture those memories now.
"He had them write down special memories of mummy on pieces of paper, cut them out and hang them on the tree in his parents' garden."
The Batley and Spen MP died after she was attacked outside a library on her way to a constituency surgery.
Bernard Kenny, 77, was discharged from hospital on Monday night after he was stabbed in the stomach as he went to the aid of Mrs Cox.
A petition to the Cabinet Office calling for Mr Kenny to be awarded the George Cross has gained over 27,000 backers.
Rachel Collinson, who started the petition and is a Green Party spokesperson, said the move would "draw the nation together to celebrate rather than to give in to fear".
She said: "This man is a ray of light in a dark time, in a moment where the UK seems to be troubled by fear and division. This guy can be a beacon for all of us in what he did."
A Cabinet Office spokesman said: "The government is of course aware of the calls for Bernard Kenny to receive an honour and we will examine the evidence, which will then be considered by the honours committee to decide whether to recommend him for an honour."
Thomas Mair, 52, from Birstall, faces charges of murder, grievous bodily harm, possession of a firearm with intent to commit an indictable offence and possession of an offensive weapon in connection with the attack on Mrs Cox.
The husband of killed MP Jo Cox has praised the public's "incredible generosity" after a fund set up in her memory hit £1m in donations.