The first murder of the year happened just a few hours into 2020, when Isaiah Usen-Satchell was stabbed to death close to his home in Norfolk Park.
Two men have been charged over his death.
Just a week later, two-year-old Keigan O’Brien died in Doncaster after being admitted to hospital in cardiac arrest.
A post mortem examination revealed the toddler had suffered head injuries.
His mum Sarah O’Brien, 32, and her boyfriend Martin Currie, 36, have been charged with murder.
The most recent death to trigger a murder probe was that of 39-year-old Leighton Owen, who was found dead in a flat in Hatfield House, Grove Place, Balby, Doncaster, shortly after 11pm on Wednesday, August 26.
Two women, aged 45 and 40, and a 21-year-old man, were arrested on suspicion of murder and later released under investigation as enquiries continue.
Anyone with information about any of the deaths should call South Yorkshire Police on 101 or Crimestoppers on 0800 555111.
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9. 9) Unascertained
Amanda Sedgwick, 49, was found dead at a property in Manor Way, Askern, Doncaster, on May 19. A 48-year-old man arrested on suspicion of murder has since been released under investigation while enquiries continue. Photo: Claire Lewis
10. 10) Head injury
Michelle Morris, 52, died on May 27 - three days after suffering a head injury in a disturbance in a house on Ramskir View, Stainforth. Two men, 47 and 33, and a 24-year-old woman arrested on suspicion of assault were re-arrested on suspicion of murder and bailed. Photo: Claire Lewis
11. 11) Assault
Stephen Georgeson, 32, died after suffering a serious head injury in a suspected attack in the Houghton Road area of Thurnscoe, Barnsley. He was found injured on Friday, June 5 and died two days later. A number of arrests have been made. Photo: Claire Lewis
12. 13) Unascertained
On June 8, the body of a 28-year-old woman, who has not yet been named, was found in a property on Main Street, Mexborough, Doncaster. Two men were arrested over the death. Photo: Claire Lewis