The Federal Trade Commission (FTC) said it could find no evidence to back claims the search engine giant "fixed" its searches.
The 19-month investigation, which amounted to nine million pages of documents, ended in agreement that Google will change some of its practices.
The search engine has said it will stop "scraping" (using snippets of) reviews and other data from rivals' websites for its own products.
Websites will now be allowed to opt out of being "scraped" without being demoted in searches.
Google has also said it will allow greater access to its Motorola patents and will use a neutral third-party to try to resolve disputes before opting for an injunction.
However, the agreement has largely been interpreted as a mild rebuke, rather than the slap that many of the search engine's rivals had been hoping for.
Making an announcement at a news conference, the FTC chairman, Jon Leibovitz, said that Google was "unquestionably one of America's great companies".
He said: "Many of Google's competitors wanted the commission to go further and regulate the intricacies of Google's search engine algorithm.
"Today, the commission has voted to close this investigation unanimously. Although some evidence suggested Google was trying to eliminate competition, Google's primary reason for changing its look and feel or algorithm was to improve search results."
Google posted a triumphant response in a blog , detailing the agreement and saying: "The conclusion is clear: Google's services are good for users and good for competition."
But Beth Wilkonon, a lawyer hired by the FTC to help steer the investigation, said: "Undoubtedly, Google took aggressive actions to gain advantage over rival search providers. However, the FTC's mission is to protect competition, and not individual competitors."
The European Commission is investigating Google over allegations of anti-competitive search practices and is due to report back later this year.
The FTC announcement came as the US State Department hit out at Google for being "unhelpful" after its executive chairman, Eric Schmidt, made a trip to North Korea.
State Department spokeswoman Victoria Nuland said: "We don't think the timing of this is particularly helpful." She said that Mr Schmidt had been made aware of US concerns about the trip.
She cited North Korea's launch of a long-range rocket in December, which raised tensions in the region.
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