The cow, nicknamed Bessie, was one of three that escaped from Rising Sun Country Park in North Tyneside on Sunday.
A helicopter and six police marksmen tracked the trio - two were recaptured but Bessie was shot "in the interests of public safety".
The vigil is to take place at 18:00 BST on Friday, at a field in Chicken Lane, Wallsend.
Thousands of people have liked a Facebook page set up in her memory.
Those attending the vigil are asked to wear a cow onesie and bring a candle.
Dave Turner, who set up the R.I.P. Wallsend Cow Facebook page, said: "It's not every day you get a cow getting shot in a field nearby. I think we need to mark this occasion with a serious send-off for Bessie.
"It wasn't doing anything, it was just eating a bit of grass - it probably got sick of the grass it was eating elsewhere, it heard about a nice new patch, went down and started grazing, and the next thing is police turn up and start firing at it.
"We are going to light candles and say a little prayer for her."
Photographer John Millard witnessed the cow being shot dead, and described the scene to BBC Radio 5 live.
He said there was a "massive police presence" with more than 15 police vehicles, a helicopter hovering overhead, and three or four officers in sniper gear.
He originally thought it could have been terrorist-related, rather than, as he then realised, a "docile little cow standing in a field".
A Northumbria Police spokesman said Bessie was destroyed after becoming "increasingly distressed" and "causing dangerous and severe obstructions" on a major road.

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The 42-year-old, who passed the mark of Cape Horn on Christmas Day after 48 days at sea, is behind only race leader Armel Le Cleac'h.
The Welshman is aiming to become the first Briton to win the race.
Thomson had led for the majority of the race but was overtaken by Le Cleac'h when he suffered a damaged foil.
The leaders are now well up their South Atlantic ascent and, after rounding Cape Horn, the skippers begin their journey north back across the Atlantic towards the finish port at Les Sables-d'Olonne.
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Thomson regained the lead in the round-the-world race north of the Kerguelen Islands in the Indian Ocean on 30 November, but has since lost ground.
He  broke two race records prior to being overtaken, as he reached the Cape of Good Hope in record time.
The Vendee Globe takes place every four years. Since the first race in 1989, only 71 of 138 starters have completed the voyage, which is known for being one of the most gruelling sporting challenges in the world.
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A memorial vigil will be held for a cow that was shot dead by police marksmen.
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Alex Thomson is attempting to overturn a deficit of about 140 miles in the Vendee Globe Trophy, with the leaders now past the halfway point of the race.