Princeton Election Consortium

A first draft of electoral history. Since 2004

Minimum population for a filibuster

In the Senate, 41 out of 100 votes are enough to block action on legislation under current rules. Those can be found in as few as 22 states. Here is the PEC electoral cartogram with the 22 smallest-population states shaded.
This gives a visual idea of the population of the states necessary to block action: 35 million out of 313 million (2012 figures). It’s not quite proportional to population because electoral votes are allocated as a combination of House (population) and Senate (2 per state). But it’s close enough to give an idea.