National Congregations Study is an ongoing national survey effort to gather information about the basic characteristics of America's congregations. The first wave of the NCS took place in 1998; Wave II was fielded in 2006-07. Online analysis options are available through this website.
Summaries of Congregational Research - this webpage from the Hartford Insitute for Religion Research offers summaries of major research projects which have the congregation as a focus of study.
U.S. Congregational Membership Reports are provided by the Association of Religion Data Archives (ARDA). These online reports are based on data from the Glenmary Research Center. The data is available in the archive.
The U.S. Congregational Life Survey was conducted in April 2000 by surveying a nationally representative sample of about 300,000 worshipers in over 2,000 congregations covering the attitudes, opinions, and perceptions of worshipers. The survey was sponsored by the Presbyterian Church, the Lily Endowment, and others. Sample excerpts from the study are available online. Data from this survey are available in ARDA.
This series was called the Yearbook of American Churches from 1952-1972 and the Yearbook of American and Canadian Churches from 1973-present. Includes membership statistics and selected statistics of church finances. Issued by the National Council of the Churches of Christ in the USA.