The US-population is growing ever since. GDP-Growth is achieved via productivity growth, but also due to more people producing a higher output (GDP). In the U.S.A. the population more than doubled from the year 1950 until now.
current US-population figures: http://www.worldometers.info
In following chart one can see the comparison year-over-year between GDP-growth and population-growth in the US:
If you prefer numbers more to graphs and curves, have a look at following table from the year 1990 up to 2016. The U.S. population is growing by over 2 mio. people per year (the median age is rising! the percentage of the urban population also!). These developments have important implications for the next 10 to 20 years! and -of course- beyond.