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.
A memorial vigil will be held for a cow that was shot dead by police marksmen.