A state’s population size typically determines how many area codes it gets. After all, area codes were invented so individuals could have personal phone numbers. With a limited amount of options in seven-digit phone numbers, area codes make it possible for telephone companies to serve nearly 1,000 times more people.

Bell Labs developed the area code system for North America during the early 1940s. Like most states, Alabama received its first area code (205) in 1947. The state didn’t get another area code until 1995, when it was assigned 334. In 1998, the state added 256. In 2001, it received 251. The 938 area code was added in 2010.

Interestingly, you can see how Alabama’s population growth affected the roll out of new area codes. In 1950, the state had a population of about 3.06 million people. By 1990, it had more than 4.04 million residents. The number swelled to 4.45 million by 2000. All of these new people needed more area codes so they could have personal numbers.

Look at this infographic from CheckThem to see where the state has placed each area code. You’ll see that the area codes serve high-population areas. The 205 area code, for instance, serves Birmingham and Tuscaloosa. The 256 area code applies to phone numbers in the Huntsville-Decatur area.

People don’t often take the time to think about how area codes describe population changes. When you look at Alabama, though, it’s easy to see how the growing population affected the placement of new area codes.