At least 53 percent of voters have voted against Proposition 2.
The proposition asked taxpayers to approve a $217 million bond to convert the former football stadium into what officials called "The New Dome Experience."
Houston-area leaders have said the so-called "Eighth Wonder of the World" would likely have to be torn down if the ballot measure failed to pass.
"Clearly, on the issue of the dome, the voters have rejected the proposal and the propose bond issue and so Commissioners Court will have to make a decision as to where we go from here," Harris County Judge Ed Emmett said.
The referendum had called for creating 350,000 square feet of exhibition space by removing the interior seats and raising the floor to street level. Other changes included creating 400,000 square feet of plaza and green space on the outside of the structure as part of the project, dubbed "The New Dome Experience."
A coalition of local and national preservation groups as well as a political action committee had banded together to try to convince voters the stadium, one of Houston's signature structures, should be reborn and not razed.
The pro-Astrodome groups took to Facebook and Twitter and spoke at community meetings. In the two weeks leading up to the election, they also drove around the county a 26-foot-long truck dubbed the "Dome Mobile," where people wrote their favorite Astrodome memories and preservation messages on a large interior wall.
While there wasn't an organized effort against the referendum, some opponents had said the money to refurbish the Astrodome could be better spent on other projects.
Studies in recent years have estimated the cost of demolishing the Astrodome to be between $29 million and $78 million.
Opened in 1965, the Astrodome was home to MLB's Houston Astros and the NFL's Houston Oilers. It was spacious enough to fit an 18-story building under its 208-foot high roof. The stadium was also home to the city's rodeo and hosted concerts and other events, including the "Battle of the Sexes" tennis match between Bobby Riggs and Billie Jean King in 1973.
But it hasn't been home to a sports team since 1999 and has been closed to all events since 2009. While still structurally sound, the iconic stadium had fallen into disrepair. On Saturday, thousands of people bought stadium seats, pieces of AstroTurf and other items at a "yard sale" and auction of Astrodome memorabilia.
The stadium's most prominent use in recent years was as a shelter for Louisiana residents displaced by Hurricane Katrina in 2005.
The Associated Press contributed to this report
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