Why do so many black women head up the households in America?

Tabithap, I think maybe the other answerers misunderstood the question. If I understand you correctly, you want to know why the proportion of "female heads of household" is greater in Census data than "male heads of household" within the black community.

First of, the Census language is sexist. It does not recognize a category of "couple as head of household." All households headed by adult male and an adult female in a marital or quasi-marital relationship are automatically called "male head of household." Only households with a single mother, or widow, or a woman living alone are designated "female head of household." Pretty annoying! Not only does it perpetuate sexist stereotypes, it presents a false view of reality by making it hard to sort out male-headed households from couple-headed households.

Ever since the 1960's, when U.S. Senator Daniel Patrick Moynihan scored big points by blaming crime, poverty, and more on the existence of black women raising families alone, the actual occurrence of female HOH's in the black community versus other communities has been exaggerated in the public imagination.

The actual proportions are available from the Census:
http://factfinder.census.gov/home/saff/main.html
Clicking "people" in the left frame, and then "relationships" gets you here:
http://factfinder.census.gov/servlet/ACSSAFFPeople?_submenuId=people_11&_sse=on
then click on "marital status" to see tables by gender, and by race. You need a breakdown by race AND gender, and I couldn't lay hands on that in the time alloted for this question.

In 2005, the US had 26 million people who identified themselves as black (which does not include biracial or multiracial people). Regardless of race, we had 110 million males, and 117 million females. That is Census data for households in 2005, and doesn't count dorms, prisons, and other institutions, and kids under 15. A different page at the Census site tells us that these 227 million people are spread across 111 million households. (Actually, because of rounding, the number's closer to 228 million than 227).
http://factfinder.census.gov/servlet/STTable?_bm=y&-geo_id=01000US&-qr_name=ACS_2005_EST_G00_S1101&-ds_name=ACS_2005_EST_G00_&-redoLog=false

This paragraph is not Census data, this is from studies of that data, combined with studies of other factors and databases (like health databases): although more boy babies are born than girls, the gender ratio evens out to 50/50 fairly soon, and then starts getting worse for males as they are knocked out by violence, recklessness (car accidents, etc.), war, drug use (including tobacco & alcohol), and suicide. Later in life, men continue to die at higher rates than women of medical causes (for a number of reasons too long to get into here).

To the extent that the black community is hit harder by deaths from violence, war, etc., that makes the gender balance in the black community even more lopsided than in all communities averaged together, with more women surviving than men, and therefore more female HOH's.

Another factor affecting black women as HOH's is that the United States disproportionately incarcerates black men, which also pulls them out of the general population.

Unemployment hits black men harder than men of other racial groups, and this too contributes to the number of black women as HOH's, since unemployed black men may remain in their parents' home (mother, father, or both) and be unable to establish their own household.

(Of course, this is in part reflective of the tendency of black women to marry with black men; black women marrying or partnering out of their race are not affected by the disporportionately high mortality, incarceration, and unemployment of black men).

This is only the most shallow answer to your question, but maybe it will help you get started. I hope this is what you were looking for.

LATE EDIT: Here are several sites which discuss the Moynihan report and its impact on public policies which still affect black women today, particularly arguments about "black pathology" and "black matriarchy" and the history of slavery. Some authors discredit him; some still think he had it right. I may not agree with some of these, but here's a range of views:

Explanation of why Moynihan wrote of "black pathology"
and policy now; long, detailed, thoughtful article
http://www.city-journal.com/html/15_3_black_family.html

Explanation of how Reagan Administration promoted idea of "black pathology" and other political uses of black demographic trends; very good review of who liked it, who didn't; shorter than first piece
http://www.jeanhardisty.com/essay_booksmatter.html

Helpful one-page summary of part of Moynihan report, including his belief that black wives are more dominant than white wives in couple-households
http://www.children.smartlibrary.org/newinterface/segment.cfm?segment=1805

A more critical, political, and detailed history of why Moynihan chose the sensational phrasing he did; use "next" at bottom of first page to see other 12 pages
http://findarticles.com/p/articles/mi_m1316/is_n5_v23/ai_10746066