The exact number of same-sex married couples in the U.S. is unknown (the Census Bureau is still working toward making improvements to this measurement), but federal tax returns provide perhaps the closest estimation. After all, about 96 percent of married tax filers file jointly, according to the Tax Policy Center. A new report from the center estimates in 2015 — the year same-sex marriage was legalized across the U.S. — there were 250,450 same-sex married tax filers (about 0.48 percent of all married tax filers), up from about 131,080 in 2013 and 183, 280 in 2014 (when same-sex marriage was only recognized in some states).

"Same-sex joint filers are generally younger, higher income, less likely to claim dependent children (especially for male couples), and more geographically concentrated than are different-sex filers," according to the Tax Policy Center's new report.

While married same-sex couples tend to have higher incomes, the income of male couples was more than 40 percent higher than that of straight couples and female couples. The average adjusted gross income of male couples in 2015 was about $165,960, versus $118,415 for female couples and $115,210 for different-sex couples. Male same-sex couples with dependent children had an average income of $264,000, more than double that of female couples and straight couples with dependent children.

Same-sex couples, the report notes, are more likely to be of working age and to live in major metropolitan areas and coastal states where incomes and living costs are relatively high.

When the data broken down by state (and the District of Columbia), D.C. is the breakaway winner with same-sex couples making up 4.17 percent of all married couples, followed by Massachusetts and Vermont, which both came in at 0.99 percent. North Dakota came in last at 0.13 percent.

The report also broke down the data by city (technically U.S. Community Zones, or CZs) to find those with the largest share of same-sex married couples. Here's the report's top 10 list:

1. San Francisco, CA

The San Francisco skyline in May 2015. David Paul Morris / Bloomberg via Getty Images file

13,220 married same-sex couples (1.52 percent)

The percentage of same-sex marriages in this LGBTQ-friendly city is nearly 12 times the the rate of Provo, Utah (0.13 percent), the city with the lowest share of married gay couples.

2. Santa Rosa, CA

Pinot noir vineyards along Mark West Station Road are turning a golden color on October 7, 2017, near Santa Rosa, California. George Rose / Getty Images

1,416 married same-sex couples (1.25 percent)

Known for its wineries, this northern California city was included in US News’ 2016 list of top "20 Retirement Communities for LGBT Seniors."

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3. Seattle, WA

Seattle's Space Needle and the downtown skyline. Carl Larson / Getty Images

9,281 married same-sex couples (1.09 percent)

Seattle is one of the cities with the largest number of same-sex female couples, totaling 2,112 in 2015. In November 2017, the city elected its first lesbian mayor: former U.S. Attorney Jenny Durkan.

4. Boston, MA

The Boston skyline Charles Krupa / AP file

9,458 married same-sex couples (1.04 percent)

Massachusetts was the first state in the union to legalize same-sex marriage. It did so in May 2004, more than 10 years before gay marriage became legal across the U.S.

5. Portland, OR

Portland, Oregon Portland Oregon Tourism Bureau

4,006 married same-sex couples (0.97 percent)

Portland is one of the few U.S. cities where the number of female marriages (1,584) outnumbers the number of male marriages (1,049).

6. Miami, FL

Downtown Miami's skyline on Friday March 11, 2016. Andrew Innerarity / for NBC News

5,131 married same-sex couples (0.92 percent)

Chock-full of gay nightlife, LGBTQ events and beautiful beaches, Miami was labeled the "greatest gay destination in America" by Thrillist last year.

7. Albuquerque, NM

Hot air balloons soar over the Rio Grande during the Albuquerque International Balloon Fiesta on October 4, 2008 in Albuquerque, New Mexico. Christian Petersen / Getty Images

1,248 married same-sex couples (0.90 percent)

Albuquerque was ranked as one of the most LGBTQ-friendly retirement places in 2018 by SeniorAdvice.

8. San Diego, CA

The San Diego Convention Center, with its sail-like roof, is surrounded by the downtown skyline, Embarcadero Park (foreground), the Marriott Marina, and San Diego Bay. Joan C. Fahrenthold / AP

4,845 married same-sex couples (0.88 percent)

This LGBTQ-friendly city was the first city in America to have a street named after gay civil rights icon Harvey Milk.

9. New York, NY

New York Skyline, Manhattan, Summer night, then the Twilight start to show over the Buildings. Tobias Ackeborn / FlickrVision via Getty Images file

13,892 married same-sex couples (0.84 percent)

New York, America’s most populated city, has the largest number of same-sex marriages in the U.S. at 13,982.

10. Portland, ME

A fishing boat leaves the dock on July 21, 2012 in Portland, Maine. Justin Sullivan / Getty Images

1,111 married same-sex couples (0.83 percent)

While it may not get the gay-friendly credit often bestowed upon cities like San Francisco and New York, Portland was voted the eighth "gayest city in America" by The Advocate in 2012.

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