Officials did not say there was any connection between the three shootings.
In Kissimmee, a community south of Orlando, Florida, two officers came under fire after approaching a group of people based on suspicions they might be involved in illegal conduct, Kissimmee Police Chief Jeff O'Dell told reporters.
The two officers, who were in uniform, appear to have been taken by surprise when they came under fire, he added. Police later arrested a suspect, whose name was not released.
The two officers were rushed to a hospital but one of the men, Officer Matthew Baxter, died of his injuries.
"Tonight we lost a brave officer - Matthew Baxter. Husband/father/hero," Florida Governor Rick Scott said on Twitter.
The other officer, Sergeant Sam Howard, was in "grave, critical condition and the prognosis does not look good," O'Dell said.
The neighbourhood where the shooting occurred has a problem with drug dealing, O'Dell said, and before the shooting the two officers approached the group of people to ask them questions.
Aside from the main suspect, police took two people at the scene into custody for questioning, he said.
President Donald Trump said in a statement on Twitter, "My thoughts and prayers are with the @KissimmeePolice and their loved ones."
In another shooting in Jacksonville, Florida, a group of officers came under fire as they walked toward a house where a man with a high-powered rifle was threatening three people inside, Jacksonville Sheriff's Office Director Mike Bruno told reporters.
The man opened fire through the door, then exited and exchanged gunfire with the officers from the Jacksonville Sheriff's Office, wounding one officer in the hands and another officer in the stomach, Bruno said.
The suspect, whose name was not released, was fatally shot in the gunfight, police said, and one officer was hospitalized in critical condition while the other was listed as stable.
In a third shooting, two Pennsylvania State Police troopers were wounded in an exchange of gunfire with a suspect at a market in Fairchance, Pennsylvania, according to local media.
The suspect died, according to Pittsburgh television station WPXI, which cited unnamed police sources. The two state troopers were in stable condition, according to local media.