That startling statistic and prediction comes courtesy of Javelin Strategy & Research of Pleasanton, California.

A boutique research firm known for its bank technology coverage, Javelin published a paid report today on tablets and their impact on mobile consumer banking. I was able to read the report and interview the primary author, Javelin research director Mary Monahan.

Javelin’s findings and predictions are based on two surveys of more than 5,000 consumers each last October and December.

It found that among the 16 million U.S. tablet owners, 42% owned an Android tablet. While iPads still led (55%), the lead was far smaller than every other estimate I’ve seen. Forrester Research, for instance, found last September that the top 3 Android tablet makers at the time – Samsung, Motorola and Acer – combined held only 12% of the U.S. market.

“Piece by piece, Android tablets have a pretty big share of the market,” Monahan said.

Because respondents could indicate if they owned more than one tablet, Javelin’s total added up to 119%. Dividing 42 by 119, Android really had closer to 35% of the U.S. tablet market.

(Here’s my post with charts compiling other analyst forecasts for the global tablet market. And here’s a list of large enterprise Android tablet deployments.)

Of course, Amazon’s Kindle Fire was not available when Forrester did its survey last September. According to Javelin, 10% of American adults had a Kindle Fire in December.

Bolstered by the Kindle, Javelin predicts that Android will eventually overtake the iPad, though it doesn’t say when.

“For the future, Google Android is expected to continue to gain consumer market share at Apple’s expense, until it takes the lead. While Android’s gains have come at the expense of profits, price-cutting is an established platform strategy that has paid big dividends in the past. Although Apple is clearly the innovator, the sheer number of Google Android tablets, price ranges, and carriers will soon prove overwhelming,” according to the report.

Meanwhile, Windows tablets also held a surprisingly high 10% of the market as of December.

For future purchases, iPads still lead (36%). Android, including the Kindle, ranked 2nd (27%), followed by perhaps surprising interest in Windows tablets (21%).

Blackberry PlayBooks had 9%, but future interest among consumers was only 4%.

Other interesting tablet statistics:

-17% of U.S. mobile phone users, or 34 million Americans, will own a tablet by the end of the year.

– Tablet adoption is forecast to grow at a CAGR of 40.3% to 40% of all U.S. smartphone users by 2016, or 87 million adults. That compares to Forrester’s forecast of 112.5 million adults by 2016.

Banks investing in new features

Javelin, naturally, honed in how consumers are using tablets to bank.

Due to its large screen, tablets are indeed becoming a popular way to bank, with 44% of tablet owners having banked via tablet or smartphone in the last 90 days.

Mobile Web sites are more popular than banking apps today, says Monahan, though that could be a function of supply rather than demand. While about 90% of banks have apps for iOS or Android, only 4% have one optimized for Android tablets (as opposed to smaller smartphones), while only 20% had an iPad-specific app.

As a result, consumers are still mostly using tablets to look up information on their accounts, rather than do transactions or pay bills, Monahan said.

Monahan cited USAA, Bank of America and Citi as having created good mobile banking apps. This year, she expects larger banks to invest in new features such as remote deposit capture (depositing checks via tablet or smartphone) and inter-bank payments to other individuals, while smaller banks roll out their apps for the first time.