Americans hold many different beliefs about the characteristics of God, but the belief that God is a person rather than an impersonal force is one of the most common. According to a 2011 PRRI poll, 70% of Americans say that the statement "God is a person with whom people can have a relationship" comes closest to describing their view of God. It's unlikely that any other attribute of God would achieve that much agreement.
The Public Religion Research Institute and the Religion News Service conducted a survey on Americans' views about God in the wake of the 2011 earthquake and tsunami in Japan. When asked what comes closest to their view of God, people answered:
God is a person with whom people can have a relationship: 70% God is an impersonal force: 17% I do not believe in God: 8% Other: 2% Don't Know / Refused: 3%
The idea that God is a person with a personality, intentions, desires, attitudes, goals, etc. is fundamental to most American conceptions of God and is arguably a prerequisite for other popular attributes. Would it really make much sense to talk about God being omniscient, for example, if God weren't already assumed to be a person?
What's more, being a person means that people can have a relationship with God — and most are convinced they already do. Christians are the most vocal when it comes to claims about having a personal relationship with God but the idea didn't start with them. Jewish scriptures depict humans interacting with God in a way that suggests personal relationships: arguments, conversations, making deals, etc.
Nevertheless, the idea that God is not only a person, but a person with whom humans can have a personal relationship is still largely a Christian doctrine and these numbers demonstrate the degree to which theism in America is really just variations on a basic Christian form of theism. It's not monolithic, but the nature of variation is rather limited.
This survey was by the Public Religion Research Institute was done with phone interviews of 1,008 adults between March 17 and March 20, 2011. The margin of error is +/- 3%.