at least 1000000
In 2005 there were 241,000,000 Cars registered in the US.
2 mine and yours
Yes, there are many US citizens who have cars, but there are many US citizens (like those who are children, those who can't afford cars, etc.) who do not have cars. There are over 250 million registered motor vehicles in the US.
In 2005 there were 241,000,000 Cars registered in the US according to the 2007 Statistical Abstract of the United States http://www.census.gov/compendia/statab/files/enercomm.html
In 2013, there were 254.4 million registered cars in the United States. That does not take into account all the cars that are unregistered or wrecked.
Gun owners aren't "registered" like cars. One estimate is that there are @ 4 million or so gun owners.
There are approximately 250 million registered cars in the U.S. There are probably another 5 million that are stored or just sitting. This is only cars and not trucks and buses.
There are 254.4MM registered cars in the US according to a 2007 DOT study. The US Census estimates there are ~310MM people in the US as of 7/2010. I'm not sure how many are citizens - perhaps ~300MM for a round number. That means ~0.85 registered vehicles for every man, woman and child in the US (or 85 vehicles per 100 people)
There were approximately 638 Chinooks registered in the US in 2009. There is no official information as to how many are registered in 2013.