[Update (6/30/10): Serious questions have been raised about the validity of Research 2000’s polls. The results below should thus be viewed as potentially suspect until the matter is resolved.]

Via Matthew Yglesias and Taegan Goddard, a new Daily Kos-sponsored poll from Research 2000 finds that only 77% of Americans, and 42% of Republicans, believe Obama was born in this country — a result that suggests the Obama birth certificate myth has circulated more widely than previously thought.

Here are the details:

Research 2000 for Daily Kos. 7/27-30. All adults. MoE 2%

Do you believe that Barack Obama was born in the United States of America or not?

Yes      77

No       11

Not sure 12

And here are the partisan and regional breakdowns, which show that the false belief that Obama was not born in this country is most commonly held by Republicans and residents of the South:

         Yes   No   Not sure

Dem       93    4    3

Rep       42   28   30

Ind       83    8    9

Northeast 93    4    3

South     47   23   30

Midwest   90    6    4

West      87    7    6

To put these numbers in perspective, we can compare them to the most recent Pew poll on the prevalence of the false belief that Obama is a Muslim (click on the chart for a larger version):

As you can see, there’s good news and bad news. The good news is that the number of correct responses is much higher on the citizenship question than the religion question. On the other hand, the proportion of incorrect answers is also much higher on the citizenship question among Republicans, which suggests that the encouragement of the birth certificate myth by conservative pundits and Republican politicians has begun to activate the GOP base on this issue. I’m not sure if Michael Steele is going to be able to make this “unnecessary distraction” go away any time soon.

(Methodological details: The chart above describes responses saying Obama was born in the U.S. or not as “citizen”/”non-citizen,” which should be interpreted as shorthand for whether he is believed to be a natural-born citizen. It also groups all responses other than “Christian” and “Muslim” from the Pew poll into a “Don’t know” category, including the 6% of respondents who refused to answer the question among the general population and the unknown proportion of Republicans who refused to do so.)

(Cross-posted with minor edits at Pollster.com)

Update 7/31 11:53 AM: I’ve rewritten this post for coherence to avoid including multiple updates.