In the years following WW2 and until the mid 1960s, the US population grew by an average 1.6% per year. From the late 1960s to 2007, it grew by an average of 1% per year. Since then, the growth rate has fallen under 1%. On my calculations, it will remain below 1% for several decades and will fall well below 0.5% in the 2030s and 2040s. Without immigration, the size of the total population would flatline or shrink moderately in those decades.
Many, or possibly most, commentators mistakenly believe that US demographic growth will be robust for decades to come. This misconception is due in part to the fact that Europe and Japan have very poor demographics in comparison to the US. The number of Europeans and Japanese is indeed expected to decline while the American population continues to grow. But the rate of US population growth will also be declining for the next several decades.