The "official" online source for information about cohousing is The Cohousing Association of the United States. This site is full of articles and notices about existing and forming projects.
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The classic book about cohousing in the United States is Creating Cohousing: Building Sustainable Communities by Kathryn McCament and Charles Durrett. These two architects studied cohousing in Denmark and continue to be the leaders of the movement in the United States. They offer consulting services through their website McCamant and Durrett Architects.
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Targeted more at Seniors, and containing much of the same material as their first book, this one is most useful to those considering senior cohousing.

On Amazon you will find several more good books on cohousing.

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