If you take a look at the wiki body count page, there does actually appear, at first glance and without exhaustive statistical analysis, to be a pattern where serial killers, as reported, seem to have been disproportionately active during the 70s & 80s. Moreover, this does not appear to be a US-only trend.
For example, of the Top 15 as listed by Wikipedia, the careers of five (Pedro Alonso López, Daniel Barbosa, Gennady Mikhasevich, Ted Bundy, John Wayne Gacy) occured entirely within the 1970-1989 interval, while the careers of six others (Pedro Rodrigues Filho, Gary Ridgway, Andrei Chikatilo, Anatoly Onoprienko, Ahmad Suradji, Serhiy Tkach) overlapped this period. It seems, from the public evidence, that 73.3% of the worst confirmed serial killers of all time were operating during this time.
This trend is apparently confirmed when one examines Wiki’s list of those with 15-30 confirmed murders. Out of this group of thirty-four, six (Juan Vallejo Corona, William Bonin, Paul John Knowles, Jose Antonio Rodriguez Vega, Robert Hansen, Dennis Nilsen) murdered exclusively during this period, while nine others (Patrick Kearney, Sergei Ryakhovsky, Joel Rifkin, Jeffrey Dahmer, Randy Steven Kraft, Robert Lee Yates, Michel Fourniret, The Monster of Florence, Charles Ray Hatcher) did so partially. Their list says that over 44% of this grouping of “the worst of the rest” were active between 1970-1989. Mind you, their list goes back to 1880.
I think, at least from a Western perspective, that the phenomenon of the serial killer may have peaked in the 70s & 80s, due to a myriad of factors, and that for us, the storm has passed.
However, the occurence of these monsters seems to have happened quite frequently in one place, in particular, over the most recent couple decades: China. A January 2012 post drew my attention to what appears to be a wave of serial killings as societal conditions change - much as happened in the West decades ago.