I'm trying to find data to answer "What is the percentage of all
married families in the US with only 1 income (either husband or
wife).  I thought I saw somewhere that it is 50 percent and I can't
find where I read that.

Dear chemstudent3625,

The most current official statistics I found were published in 2005
and relate to the year 2003. The figures are as follows:

Total number of married-couple families.......... 57,767,000 (100%)
Married-couple families with no earners..........  8,843,000 (13.9%)
Married-couple families with one earner.......... 14,051,000 (24.3%)
Married-couple families with two or more earners. 35,673,000 (61.8%)


In 10,469,000 (18.1%) of all married-couple families, the husband is
the only earner
In 3,026,000 (5.2%) of all married-couple families, the wife is the
only earner. In 557,000 (1.9%) of all married-couple families, another
family member is the only earner.

Hope this answers your question!
Regards,
Scriptor



Sources:

U.S. Department of Labor, Bureau of Labor Statistics: Married-couple
families by number and relationship of earners, 1967-2003 (PDF file)
http://www.bls.gov/cps/wlf-table23-2005.pdf

U.S. Department of Labor, Bureau of Labor Statistics: Women in the
Labor Force - A Databook
http://www.bls.gov/cps/wlf-databook2005.htm

how is there people who make no money?!?! Is it mostly elderly/retired people?

Yes, those non-earners would mostly be retired... also people between
jobs (the 4.4% unemployment rate we have) and the select few, the
proud, the married people who live at one of their parent's houses and
don't contribute a dime to living expenses.