Local fire companies were "started" at 8:45 p.m., according to the news release.
Members of the first unit from Joppa-Magnolia's Edgewood station, who arrived at 8:48 p.m., reported that fire could be seen at the rear of the three-story townhouse, according to the news release.
Joppa-Magnolia, Abingdon and Kingsville volunteer fire companies, along with the Aberdeen Proving Ground Fire Department, had initially been alerted, and fire personnel on the scene called for support.
The Bel Air and White Marsh volunteer companies sent units in response.
There were 60 volunteer firefighters and EMS workers on the scene, plus four paid APG firefighters.
Nearby Brookside Drive and Gateway Road were briefly closed; fire officials declared the blaze under control at 9:23 p.m., according to the news release.
The cause of the fire is under investigation by the Maryland Office of the State Fire Marshal, and the people displaced are receiving disaster assistance.
On Monday evening, another fire was reported at about 7 p.m. in a basement in the 900 block of Topview Drive.
The fire was noticed by a Harford County Sheriff's Office deputy on routine patrol, said Andy Doyle, spokesman for Joppa-Magnolia Volunteer Fire Company.
After calling for the fire department, the deputy went in to look for anyone inside. No people were found, but the deputy rescued a dog. The three cats in the home died, according to Joppa-Magnolia's press release.