The ranch has been open for tours since the mid-1980s and now sees more than 100,000 visitors each year. Each room of the house has a theme for each character.
On Saturday, J.R. Ewing's room had flowers and a card for tourists to sign.
"Today is about Larry Hagman and his family," said Janna Timm, a Southfork Ranch & Hotel spokeswoman. "He was such a wonderful person, and we will really miss him."
"Dallas" was recently revived on TNT this summer, and all of the scenes were filmed at Southfork or other places in the Dallas area. Hagman had revised his role as the scheming oilman who would even double-cross his own son.
Linda Sproule of Peterborough, Ontario, had been traveling through the U.S. the past couple of weeks and heard about Hagman's death Friday while in Dallas. She said she didn't know where Southfork was but wanted to come because she was a fan of the show in the 1980s.
"I remember on Friday nights we watched it, and J.R. was bigger than life in some ways," she said after taking the Southfork tour Saturday morning. "This ranch is beautiful. Being here is kind of emotional in a way."
Barbara Quinones and her husband were in town for their daughter's soccer tournament and had already planned to visit Southfork when they heard news of Hagman's death.
"We loved him because he was so ruthless," said Quinones, of Albuquerque, N.M. "This is a sad day, but I'm glad we're here."
Some of the show's stars, including Hagman, came to Southfork for the series' 25th anniversary. The Fort Worth-born actor also had visited several times before the show was revived.
"He was definitely a gentleman, a class act," said Jim Gomes, vice president of resorts at Southfork Ranch & Hotel. "He loved the fans as much as they loved him."
Five things to know about "Dallas" star Larry Hagman
1. His famous mom
Hagman was the son of singer-actress Mary Martin, who starred in such classics as "South Pacific" and "Peter Pan." Martin was still in her teens when he was born in 1931 during her marriage to attorney Ben Hagman.
2. How he first gained fame
Years before "Dallas," Hagman was on "I Dream of Jeannie," in which he played an astronaut whose life is disrupted when he finds a comely genie, portrayed by Barbara Eden, and takes her home to live with him.
3. His real life advocacy
Hagman was diagnosed with cirrhosis of the liver and acknowledged that he drank heavily for years. He had a transplant after a malignant tumor was discovered in 1995, and it turned him into an advocate for organ donation and a hospital volunteer. He was also an anti-smoking activist who took part in "Great American Smoke-Out" campaigns.
4. What he wanted on J.R.'s tombstone
"It should say: 'Here lies upright citizen J.R. Ewing. This is the only deal he ever lost,'" Hagman said in 1988.
5. Who shot J.R.?
The answer to that cliffhanger was one of the most-watched television events in history. It was J.R.'s sister-in-law, Kristin (Mary Crosby) he had made her pregnant, then threatened to frame her as a prostitute unless she left town.