Only about 300 years, from your own link you kindly provided:
When European settlers first arrived in North America, they brought with them a number of animals that were not native to the continent. One of these animals was the eastern gray squirrel (Sciurus carolinensis), which was introduced to England in the early 1600s as a curiosity.
The eastern gray squirrel quickly became popular in England, where it was kept as a pet and admired for its agility and intelligence. In the late 1700s, a group of eastern gray squirrels was introduced to New York City’s Central Park, where they quickly established a population.
Over the next few decades, the eastern gray squirrel spread rapidly across North America, aided by its adaptability and ability to thrive in a variety of habitats. Today, the eastern gray squirrel is one of the most common squirrels in North America, and it can be found in every state except for Alaska and Hawaii.