They come as a man has been charged with her murder.
West Yorkshire Police said Thomas Mair (52) has been charged with the murder of the 41-year-old.
She was fatally injured outside her constituency surgery in Birstall, West Yorkshire.
Mr Mair will appear at Westminster Magistrates’ Court later and faces a number of other charges, including grievous bodily harm.
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He is further charged with possession of a firearm with intent and possession of an offensive weapon, the force said.
Paying tribute, Falkirk MP John McNally, who like Mrs Cox was elected to Parliament last May, said: “Our hearts go out to the family of talented young MP Jo Cox.
“She had a passion for righting injustice in the world and worked hard to highlight the needs of people who wouldn’t otherwise have had a voice.
“She has been cruelly taken from the community she grew up in and the constituency she served so well. It is impossible to contemplate the loss her husband and children now face.
“We must continue her mission to counter hate with liberty and compassion.”
Linlithgow and East Falkirk MP Martyn Day was one of many taking to social media to express his condolences.
He said: “Heartbreaking to learn Jo Cox has died after today’s attack. Thoughts are with her family at this terribly tragic time.”
Falkirk Council leader Craig Martin echoed the sentiments expressed from politicians around the world when he said: “The news that Jo Cox MP had died after a vicious attack on her outside her constituency office has come as a shock to all, not just in the Labour movement but across politics and other sectors, particulary in the third sector as Jo worked with voluntary organisations against inequality.”
He added: “To hear of such an incident when the victim was doing her community duty brings to the fore the security issues for any elected member. We pride ourselves on being available on demand, which includes holding surgeries, home visits and even being approached on the street or in a shop. To be honest I, as an elected member would not have it any other way. But such a tragedy as Jo’s reminds us of the ultimate dangers.
“I’m utterly shocked, we must feel for her husband and young family. This is an uneccesary death, of a very well liked, local and active MP.”