The 21 homicides in 2018 received much attention, with rallies and vigils. According to public data, there were 51 fatal accidental overdoses in Hartford in that same time. That number could potentially increase with completion of outstanding toxicology reports.
From the same data source — police incidents, 2015-current — there were at least 42 non-fatal overdoses in Hartford; the non-fatal stats seem incomplete, but I am including this to give an idea of how this problem is spread across the city. The fire department (EMS crew) responds to numerous medical calls daily, but they do not provide as detailed of data as the police department. Some entries were found in both data sets.
A few items to note while interpreting data: the red icons with skull & crossbones represent fatalities; purple icons with medical bags represent non-fatal overdoses.
Although some of these events may have happened indoors, it should not be assumed to be the case for all as overdoses occur on sidewalks, in parking lots, and inside vehicles parked on the street in front of buildings and homes that the victims have no personal connection to. Data does not indicate if the victims were from Hartford or elsewhere.
While zooming in on the map, you will find multiple icons stacked on a few locations. That is not a mistake. A fast food restaurant on Washington Street and a hotel on West Service Road are sites of several overdoses.