Tesla currently has 373 Superchargers in North America, but their goal is to double the number by the end of the year, the company has stated in their investor letter.
Tesla clearly wants to expand their Supercharger network, and they already started the expansion in January.
Tesla's Superchargers were free up until the beginning of this year. Any customer who buys a Tesla car after January 1st, 2017 will have to pay a small fee when filling up at a Supercharger station. However, they will also be supplied with 400 kWh of free Supercharging credits each year, good for about 1,600 kilometers.
According to Tesla's website, the company has 805 Supercharger stations worldwide and 5,159 chargers.