The Fed has data on household finances dating back at least to the 1950's. They track the balance sheets of households and non-profit organizations. The latest balance sheet shows that assets are about $67.4 trillion, liabilities are $13.9 T giving us a net worth of $53.5 T.
Lets look at household balance sheet over history.
Here is the big picture from 1952 to 2010 showing the household assets, liabilities and net worth in trillions of dollars:
Lets zoom in to just 1980 to 2010:
You may notice that the debt line is going up faster than the asset line. While net worth is still pretty high, the amount of debt we have versus our assets is increasing. Here is the ratio of debt / assets:
Keep in mind that this data is the total sum of all money held by American households and non-profit organizations. This is not a good reflection of typical American households finances. THe data does include all the assets and liabilities so all of the real estate we own and our mortgages plus things like the pension funds held by non profits and other things that aren't really part of typical households.