His bond was previously set at $2 million. Johnson is scheduled to be arraigned on Tuesday.
Johnson is accused of killing his ex, 38-year-old Marquia Hunter, at her Dayton apartment on March 16.
Around 11:21 p.m., a man called 911 and said he heard gunfire.
He said he thought his friend was shot and on the ground outside City View Terrace apartments, according to Montgomery County Regional Dispatch records.
He said she had previously told him she was going through domestic violence issues.
Dayton police arrived and found Hunter dead in the driveway.
Investigators identified Johnson as the suspect through witness statements, cellphone analysis and surveillance video.
Hunter had an active protection order against Johnson and he had previously been convicted for violating a protection order, according to the prosecutor’s office.
Johnson is being held in the Montgomery County Jail.
Anyone experiencing domestic violence can contact Dayton’s Artemis Center at 937-461-HELP (4357) or the National Domestic Violence Hotline at 1-800-799-SAFE (7233).