It is a common notion that the number of priests has plummeted in this country. Many speak of the halcyon days when there were four and five priests per parish, and the seminaries were packed. And while some of these memories are accurate, they are drawn from a time in this country that was very brief.
The fact is, the number of priests per parish spiked sharply after 1950 and has now leveled back to the levels of 1950 and before.
Note the graph at the upper right from the Center for Research in the Apostolate (CARA). It depicts the number of priests per parish. In 1950 there was an average of one priest per parish. Last year there was an average of one priest per parish. Welcome to 1950.
Mark Gray, writing at the CARA blog says:
There was about one active diocesan priest per parish then as there is now. The late 1950s into the 1970s represent an exceptional period in American history when there were significantly more active diocesan priests available than there were parishes. Age and mortality has and continues to diminish the size of the diocesan clergy population. Although ordinations have remained stable for decades, these are not sufficient to make up for the number of priests lost each year to retirement or death. 
Frankly, even in the glory days, America did not produce the number of priests we need to fill our needs. Back in the 1950s through the 1970s a tremendous number of FBI (foreign born Irish) priests were enlisted to meet American needs. My own diocese had a large number of them brought in, beginning in the 1950s.
Many ethnic groups in the Urban North also brought large numbers of priests to serve them from overseas. Today there are many dioceses that rely on Nigeria and other booming Catholic countries to supply extra priests.
It is true, most American Seminaries were bursting at the seams especially after World War II. But that boom would seem to be as short as it was impressive. Here on the East Coast, Roland Park in Baltimore and St. Charles Borromeo in Philadelphia had more than 500 seminarians in mammoth buildings that looked like Versailles as you drove up.
But as the graph shows, the spike was sudden and has settled back to the more common US experience of about one priest per parish. Again, according to the CARA study:
Nearly one in five U.S. parishes do not have a resident priest pastor. Seven in ten have a diocesan priest serving in this capacity and religious priests serve as resident pastors in 11% of parishes. In 17% of parishes a priest is serving as a non-resident pastor…in 2.5% of all parishes, due to a shortage of priests, a deacon or lay person is entrusted with the pastoral care of a parish…[who]….must still do their best to arrange for priests to be available for Masses and other sacraments.
Priests cannot be in two places at once and there are only so many hours in a Sunday. We have a good understanding of how many parishes there are in the United States and how many priests are available. The map below (click for full size) shows the number of active diocesan priests subtracted from number of parishes in each diocese…. In 60% of dioceses, those marked in yellow and red, there is no surplus of diocesan priests active in ministry relative to the number of parishes in the diocese. The green areas on the map have more active diocesan priests than parishes. 
There is more that can be read at the CARA blog that analyzes these numbers more deeply. But data like this reminds us that our knowledge of history is at time inaccurate since it is based on a rather narrow sliver of our own experience. That the Catholic Church in America grew enormously in the first half of the 20th century is indisputable. This was due to large waves of immigrants from Catholic Countries in Europe that were in one crisis after another. But even at the center point of that remarkable period of Catholic growth, the number of priests per parish was not so high as we remember, and even after it spiked (nearly doubled) between 1950 and 1960, it did not last, and a long leveling back to our current numbers has restored us to the mid century mark.
And yet, 1950, would be a year most Catholics think of being a high water mark. It was not, at least in terms of the number of priests per parish. Yes, welcome to 1950.