Yeah, the collapse in crime is a national thing, not a New York thing.
How many people were murdered in the US last year?
14,196. Lowest total murder total and the murder rate of 4.5 per 100,000 citizens is actually the lowest since the government began keeping track of the statistic.
Out of curiosity, when did the government begin keeping track of the statistic?
I'm not really sure. Sometime around Prohibition era when crime became a national issue I imagine. I can find some sites with data back to 1900 but I don't know if those old numbers are government data or independent. The 1900-15 murder rates are comically low (~1 murder per 100,000) before jumping to 6-8 so I imagine that's poorly gathered independent data not government and government data began around the Wilson Admin.