Schools across Greater Lincolnshire received fake bomb threats on the morning of Monday, March 19.
Nationally, more than 400 schools and colleges received emails claiming that a device had been planted and demanding cash.
Lincolnshire Police said nine schools in their force area had been targeted by the threat. Humberside Police have also dealt with 19 reports in East Yorkshire and Northern Lincolnshire.
Officers have reassured parents that threats are not believed to be credible.
Lincolnshire Police said: “Nine schools in Lincolnshire have this morning reported to us that they have received a malicious communication.
“The email is a national hoax and an investigation into where it originated from will take place.
“We take hoaxes extremely seriously as they divert our resources and can cause disruption and alarm to the public.”
Detective Superintendent Tony Cockerill from Humberside Police added: “We have been liaising with our counter terrorism colleagues across the country and it is not believed that the threats are credible.
“We have spoken to all schools who have contacted us, reassured them that there is no need to evacuate and offered them security advice.”