Source: U.S. Bureau of Labor Statistics  

Release: Labor Force Participation by State  

Units:  Percent, Seasonally Adjusted

Frequency:  Monthly

A state's labor-force participation rate is the number of all employed and unemployed workers divided against the state's civilian population.

Differences between monthly seasonally-adjusted and not-seasonally-adjusted labor force participation rates are determined by the seasonal components of the LAUS labor force levels.

The not seasonally adjusted version of this time series is LBSNSA48

Source: U.S. Bureau of Labor Statistics  

Release: Employment Situation  

Units:  Percent, Seasonally Adjusted

Frequency:  Monthly

The series comes from the 'Current Population Survey (Household Survey)'
The source code is: LNS11300000

The Labor Force Participation Rate is defined by the Current Population Survey (CPS) as “the number of people in the labor force as a percentage of the civilian noninstitutional population […] the participation rate is the percentage of the population that is either working or actively looking for work.”

The Labor Force Participation Rate is collected in the CPS and published by the BLS. It is provided on a monthly basis, so this data is used in part by macroeconomists as an initial economic indicator of current labor market trends. The labor force participation rate helps government agencies, financial markets, and researchers gauge the overall health of the economy.

Note that long-run changes in labor force participation may reflect secular economic trends that are unrelated to the overall health of the economy. For instance, demographic changes such as the aging of population can lead to a secular increase of exits from the labor force, shrinking the labor force and decreasing the labor force participation rate.

For more information, see:
U.S. Bureau of Labor Statistics, CES Overview
U.S. Bureau of Labor Statistics, Concepts and Definitions (CPS)