The impact of increasing the length of unemployment benefits on how long the unemployed are out of work: Figure 3

See this page from the Bureau of Labor Statistics for information on the percent of the unemployed who have been unemployed for at least 26 weeks.
See p. 33 of this study for the Average Maximum Duration of Unemployment benefits from 1954 to 2003.
See these links here, here, and here for more recent changes in the Average Maximum Duration of Unemployment benefits.