The share of mortgage properties in the United States considered to be "equity rich" increased slightly from a year ago, according to the real estate data site RealtyTrac. The same period also saw a reduction in the share of homes considered to be seriously underwater on their loans.

RealtyTrac defines an equity rich property as one where the loan-to-value ratio is 50 percent or lower, indicating that the owner has built up at least 50 percent equity in the home. Seriously underwater homes are defined as having a loan-to-value ratio of 125 percent or more, where the amount owed on the property is at least 25 percent greater than the estimated market value.

There were 10.9 million homes considered to be equity rich in the second quarter of 2015, accounting for 19.6 percent of mortgaged homes in the United States. This marked a slight decrease from the first quarter, when there were 11.1 million equity rich homes representing 19.8 percent of all mortgaged residences, and the fourth quarter, when there were 11.3 million equity rich homes representing 20.3 percent of all mortgaged homes. However, it was up from the second quarter of 2014, when there were 9.9 million equity rich homes – 18.9 percent of all homes with a loan.

"The number of homeowners with a mortgage who have at least 20 percent equity has dropped by more than 900,000 during the past six months, indicating that homeowners who have gained substantial equity thanks to the housing price recovery over the past three years are taking advantage of that newfound equity," said Daren Blomquist, vice president of RealtyTrac. "Some are leveraging that equity into a higher loan-to-value refinance or a move-up purchase, some may be downsizing into an all-cash purchase, and some may be cashing out of homeownership altogether. Those homeowners cashing out of homeownership altogether would explain why the nation's overall homeownership rate continued to decline in the second quarter even as homeownership rates among Millennials increased."

The report says the markets with the highest percentage of equity rich homes are in areas where home prices have seen steady growth. These areas include San Jose, California (43.8 percent); San Francisco, Calif. (38.3 percent); Honolulu, Hawaii (36.7 percent); Los Angeles, Calif. (32 percent); and New York City (30.7 percent).

RealtyTrac's U.S. Home Equity and Underwater Report for the second quarter of 2015 also indicates that there were about 7.44 million seriously underwater homes in the nation in the second quarter. This figure represents 13.3 percent of all residential properties in the United States with a mortgage.

This share of seriously underwater homes was an increase from the first quarter, when 7.34 million homes representing 13.2 percent of homes had this designation. It was a decrease from the second quarter of 2014, which tallied 9.07 million seriously underwater homes – 17.2 percent of mortgaged properties. RealtyTrac says the share of seriously underwater homes peaked at 28.6 percent in the second quarter of 2012, representing 12.82 million properties.

"Slowing home price appreciation in 2015 has resulted in the share of seriously underwater properties plateauing at about 13 percent of all properties with a mortgage," said Blomquist. "However, the share of homeowners with the double whammy of seriously underwater properties that are also in foreclosure is continuing to decrease and is now at the lowest level we've seen since we began tracking that metric in the first quarter of 2012."

Homes purchased between 2004 and 2008 accounted for the largest share of seriously underwater homes. Thirty-eight percent of seriously underwater homes were purchased between seven and 11 years ago.

Homes owned for nine years had the highest seriously underwater rate at 21.6 percent, followed by homes owned for 10 years at 19.8 percent. Nineteen percent of homes owned for eight years were seriously underwater.

Among the markets with a population of 500,000 or more, the highest share of seriously underwater properties was in Lakeland, Florida, at 28.5 percent. Other markets with a high share of seriously underwater properties included Cleveland, Ohio (28.2 percent); Las Vegas, Nevada (27.9 percent); Akron, Ohio (27.3 percent); and Orlando, Fla. (26.1 percent).

In many of these markets, the share of distressed properties that were seriously underwater exceeded 50 percent. These markets included Las Vegas (57.7 percent), Lakeland (54.8 percent), Cleveland (52.9 percent), and Chicago, Illinois (52.5 percent).

Among distressed properties—defined as being in some stage of foreclosure—34.4 percent were seriously underwater in the second quarter of 2015. This share fell from 35.1 percent in the first quarter and 43.6 percent in the second quarter of 2014. This was the lowest share since RealtyTrac began tracking the information in the first quarter of 2012.

Meanwhile, the share of foreclosures with positive equity—those in a stage of foreclosure where the loan-to-value ratio was 100 percent or lower—increased to 42.4 percent in the second quarter of 2014. This was a jump from 42.1 percent in the first quarter and 34.1 percent in the second quarter of 2014.

Colorado had the highest share of distressed properties with positive equity at 72 percent. Other states with a significant share of positive equity homes in foreclosure included Alaska (69.8 percent), Texas (66.4 percent), Oklahoma (65.2 percent), and Nebraska (64.4 percent).

The share of distressed properties with positive equity exceeded 60 percent in several markets. These included Denver, Colo. (83.7 percent); Austin, Texas (83.1 percent); Honolulu (77.5 percent); San Jose (77 percent); and Pittsburgh, Pennsylvania (75.9 percent).

RealtyTrac's U.S. Home Equity and Underwater report collects information on several categories of equity at the metro, country, and state levels. This data also takes into account the total number of homes represented by each equity category. Equity calculations are based on available data for loans, property values, and foreclosures.