“So, we’ll go up and see the dog park,” Melanie Hallowell says, striding across the lobby to a bank of elevators, heels clicking on the marble-hard floor.

In City Market at O, the luxury rental building she manages, the canine occupancy rate is about 30 percent, or 390 leased apartments and roughly 117 pooches. Hallowell pushes “R” for rooftop and says in a heartfelt way, “We find that our residents think of their dogs as their children, so whatever we can offer them, we do.”

The open-air dog park, nine stories above Washington’s gentrified Shaw neighborhood, is 200 linear feet of artificial-turf ball-chasing space for, let’s say, Bella. And Bella might need a good work out just now, having been cooped up for hours in ... oh, say, a $4,000-a-month two-bedroom while her thirtysomething pet-parent was busy at the office all day.

The park’s adjoining dog-wash station — two small, stainless-steel shower bays with blow dryers in a white-tiled room — is another selling-point.

Like pretty much every other high-ticket residential building in town, City Market is enthusiastically pet-friendly, and it’s no wonder: Tens of thousands of newcomers, mainly affluent professionals, have flocked to the nation’s capital in recent years, many of them with animal companions.

Charity Struthers, right, holds her dog, Benny Goodman, on the roof of the Park Chelsea Apartments. (Evelyn Hockstein/For The Washington Post)

The D.C. Health Department was unable to give numbers showing the growth of the city’s dog population. But who needs them? These days, pooches are seemingly everywhere in revitalized neighborhoods, on practically every patch of grass and pavement.

Just count the ubiquitous sidewalk dog dishes, filled with Milk Bones or mineral water, in front of millennial-fashion boutiques, latte emporiums, craft-beer watering holes and other establishments.

There’s one now, at the door to East City Bookshop, which opened in Capitol Hill in the spring and where pets are welcome in the aisles.

“People are more likely to shop if they’re not worried about their dogs being tied up outside,” says Emilie Sommer, the store’s book-buyer. In the community room, “we have these pictures of our neighborhood dogs that have come to visit us.” Bone-shaped treats are set out by the cash register (“and also Hershey’s Kisses for our humans”).

Meanwhile, developers vying for residential tenants have rolled out the Astroturf.

“We saw that 40 percent of the population that rents in Washington has dogs,” says Richard Lake, one of City Market’s owners, referring to research his company did before the building opened two years ago. “If you’re trying to appeal to a broad market, you don’t want to alienate 40 percent of the rental population.”

Two such tenants are in the rooftop dog park now, sitting on a bench, tapping their phones while their fur babies frolic.

Dennis and Greg Lacot are 34-year-old identical twins who share a City Market apartment, work separately in the IT field and adore their pint-sized Italian greyhounds, Gemma and Giada, born in the same litter last year.

“We had a great picture that won them pets of the month in the building,” says Dennis, searching his iPhone for the photo. “Dual pets of the month.”

Greg says: “The building hosts pet parties. They had a — what was that? ...”

“The yappy hour,” says Hallowell.

“The yappy hour! They had, like, a little barbecue for the pet-parents, and they had treats for the dogs. And the dogs had little hats.”

Still looking for the picture, Dennis says: “There are a lot of dogs in the neighborhood, and we know a lot of them, especially the ones in the building. ... We see Rosey, we see Logan, we see Stella.” Then he says, “Here it is,” the prize-winning snapshot.

Gemma and Giada, whose narrow heads are mostly long noses, are staring into the camera in a close-up, their expressions vaguely quizzical.

“Just pride and celebrity is what you get,” Dennis says wryly.

Greg adds, “A little bio goes up in the elevator.” And his brother, nodding, says, “They were definitely a lot more popular after that.”

Dog-lovers like the Lacot brothers have been a boon for owners of related businesses, especially dog walkers.

There’s JJ Scheele, for one. She moved to Washington from San Diego in 2004, just as gentrification was turning feverish, to run a political action committee promoting the humane treatment of animals. Moonlighting as a dog-walker, “I got up to 17 dogs in nine months with no advertising, just word of mouth,” Scheele recalls. “That’s when I decided, and everyone told me, I should start a business.”

Now, as owner of Dog Walking DC, in Dupont Circle, “I have 25 to 30 independent contractors” who “do over 100 midday walks,” she says. “We have about 400 keys,” meaning customers, and “I turn away about two or three clients a day.”

Dave Liebman has had a similar experience since 2005, when he and a partner bought City Dogs, a daycare center for pooches in Dupont Circle. Business is booming, he says, and they plan to open a second location next month, inside a new apartment complex in a gentrification hotspot, Third and H streets NE, near Union Station.

“When you see these buildings that are popping up, you can just look at the rents, the pet-friendly amenities, and you know this is where you want to be,” Liebman says.

At City Market, having Gemma and Giada in their lives costs the Lacot twins $120 a month in doggie rent ($60 per greyhound) on top of the building’s one-time pet fee: $500 for a single animal, $800 for two. A mile east, at the equally swank 2M Apartments, the move-in pet fee is similar, but, after that, Rover resides for free.

Plus, for 2M renters who are too busy to own pets, there’s Emmy, a miniature English bulldog, as docile as can be, 40 pounds of folded flesh and droopy cheeks waddling around the leasing office all day, waiting for attention.

“Emmy is owned by the company,” says Kaitlyn Luper, the property manager, as her stubby-legged staffer lumbers from desk to desk. Emmy, whose business cards are at the concierge counter, is a perk for tenants, available for playdates in 2M’s dog park. “We have about 10 residents we see pretty consistently, coming to play with Emmy,” says Luper, who lives with Emmy in the building.

Mara Pillinger, a 2M tenant since 2014, says, “She’s the reason I moved in!” A doctoral student in political science, Pillinger, 31, travels for weeks at a stretch, doing research, and can’t take care of a pet. “I love dogs; I grew up with dogs,” she says. While looking for an apartment, she heard about Emmy from a friend. “I called that same day and asked to come in and see the building — and the dog. It was the perfect arrangement.”

Young professionals aren’t the only folks who have repopulated the once-shrinking city in the past decade or so. Plenty of older empty-nesters are arriving, too, including Charity Struthers, 56, who moved to Washington from Raleigh, N.C., this month.

Unmarried and with her kids gone off to college, Struthers lives with Benny Goodman, a 6-year-old black lab so named for his “perpetual tail swing.”

“I like arts, I like politics, I like history, I like architecture, and I decided that this is where I’m going to live,” says Struthers. She looked at 25 apartments over the summer, with pet-friendliness “high on my list.” And that wasn’t all she did.

“Usually you can spot dog-walkers because they have so many dogs,” she says. “So I went out and watched for dog-walkers. I would ask them what their favorite buildings were. They have a very nice angle on which ones are the best for pets.”

She wound up near the redeveloped Southwest Waterfront, in the new Park Chelsea, where one-bedrooms like hers cost up to $2,500 a month. More than a third of the building’s 235 occupied apartments have dogs in them, says manager Elizabeth Guzman. And of course there’s a rooftop park for the pooches, among other amenities.

Benny Goodman, unaccustomed to high-rise living, was a bit spooked at first by the elevator bells and recorded announcements. But Struthers reports he’s doing better now.

“And he’s making lots of friends.”