On Thursday morning, 35 officers received training on how to administer the nasal mist version of the medication. Those officers will then be used to train the rest of the force.
By the end of next week, it's expected every officer in the county will be issued a Narcan kit at the beginning of every shift.
Paramedics have long carried doses of Narcan, but with the heroin death rate rising, many police departments are starting to carry it too because they often arrive at the scene of an overdose before an ambulance or fire truck.
St. Charles County police began carrying Narcan last November.
St. Louis County had at least 90 deaths last year from heroin. Chief Jon Belmar believes if police had been carrying Narcan, they could have reduced those numbers by as many as 20 people.
The St. Louis County Health Department is paying for the Narcan supply. The initial cost is $12,000. Each dose costs $57.