ST. PETERSBURG — By the time Tamara Harrell put her key into the lock, she was dabbing her eyes with a tissue. Owning the orange house on 21st Avenue S was a major milestone for the single mother, one she earned while working full time and studying to become a registered nurse."Everything was a challenge, but you gotta do what you gotta do," said Harrell, 33, who has an 11-year-old son and a 10-year-old daughter.Harrell's home also marked a milestone for Habitat for Humanity: The nonprofit has built or restored 300 homes in Pinellas County since the local branch started in 1985. City and community leaders gathered outside the one-story house Monday morning to celebrate the achievement. "It speaks volumes to the support that Habitat has from the business community, as well as to our other partners," said Mike Sutton, the CEO of Habitat for Humanity of Pinellas County.On hand was Jane Dunaway, the recipient of the group's first home 29 years ago."So much has happened," Dunaway said as she looked over Harrell's home. "So much has changed. Each home has gotten bigger and better." Dunaway, now in her 70s, was 42 when she moved into her home on 13th Street N in St. Petersburg. She had two small children at the time."My kids helped build the house," she said. "We all put in the hours together."Dunaway, who still lives in the home, has tried to stay involved with Habitat for Humanity over the years as a way to give back.Habitat hopes to build or refurbish 200 more homes in the next four years, Sutton saidHe also announced a new home rehabilitation program that will refurbish homes in Midtown's 22nd Avenue S corridor, making them safer and more accessible with upgrades like a new roof or structural repairs. "We really want to be present at the table with everything that's going on down here," Sutton said. "It's just such a vibrant community." Harrell grew up about a block away. Her new house is on a double lot, and her sister, Dominique Baptiste, is in the process of finishing her 250 "sweat equity" hours so she can move in next door.Harrell will pay between $90,000 and $100,000 for the house over 30 years. Her monthly payments, which will include insurance and tax payments, will come out to about $500 per month. Habitat provides the mortgage at a 0 percent interest. Harrell struggled for about 18 months to finish her "sweat equity" hours on her own home and others. But the juggling was worth it, she said, because it's been hard to find a safe place for her family to live.They lived in an apartment complex that was ultimately deemed unfit to live in, and a space above a store where she spent only two weeks because a security guard was shot nearby. She earned her licensed practical nursing certification and now works at Community Health Center. A better job helped her find better housing, she said, but owning a home is the ultimate achievement."I can sit in this shady back yard and relax," she said. Claire Wiseman can be reached at email@example.com or (727) 893-8804. Follow her on Twitter @clairelwiseman.