From Kauffman Report: It Takes Decades to Build a Startup Hub:

Boulder topped the list of small- to mid-sized cities with high startup density in 1990 and again in 2010.
Boulder topped the list of small- to mid-sized cities with high startup density in 1990 and again in 2010.

Boulder topped the list of small- to mid-sized cities with high startup density in 1990 and again in 2010. Source: Dane Stangler, “Path-Dependent Startup Hubs: Comparing Metropolitan Performance: High-Tech and ICT Startup Density,” Ewing Marion Kauffman Foundation, September 2013.