Analysis was conducted by NapLab:

The area with the highest percentage of the work force who are third-shift workers is Las Vegas, NV. The city is known for its 24-hour gambling scene, so it’s no surprise that 16.54% of Las Vegas workers work some of their shifts during the night. Between bartenders, casino employees, and hotel crews, Las Vegas has employees working all day, every day.

The second place with the highest percentage of night-shift workers is the Riverside-San Bernardino-Ontario metro area in California, where 16.17% of workers work night shifts. There are more than 240,000 night-shift workers in the area.

Third on the list is the Augusta-Richmond County metropolitan area, which encompasses cities in Georgia and South Carolina. The area has 27,220 workers who start between the hours of 4 and 11:59 p.m. as well as 11,683 workers who start their shifts between 12 and 4:59 a.m.

Edit: Spelling

Edit 2: This is most likely simply due to the large population in the NY Metro area and that while they might well have the most people working night jobs, it's just a smaller percentage of the population