You can take it here.  33 questions.

The average American scored 49%.

My score was 87.88%, but I'm kind of a civics geek.

According to this article, U.S. elected officials scored lower than the average American; they scored 44%.  We'll call that "the Palin effect".  Don't read the article if you're going to take the test — it gives away some of the answers.

Some further findings (SPOILER ALERT if you haven't taken the test):

Seventy-one percent of Americans fail the test, with an overall average score of 49%.

• Liberals score 49%; conservatives score 48%. Republicans score 52%; Democrats score 45%.
• Fewer than half of all Americans can name all three branches of government, a minimal requirement for understanding America’s constitutional system.

Earning a college degree does little to increase knowledge of America’s history, key texts, and institutions. The average score among those who ended their formal education with a bachelor’s degree is 57%, or an “F.” That is only 13 percentage points higher than the average score among those who ended their formal education with a high school diploma.

• Only 24% of college graduates know the First Amendment prohibits establishing an official religion for the United States.

Officeholders typically have less civic knowledge than the general public. On average, they score 44%, five percentage points lower than non-officeholders.

• Thirty percent of elected officials do not know that “life, liberty, and the pursuit of happiness” are the inalienable rights referred to in the Declaration of Independence.