The sign in Ward 28 of a long, narrow brick building is a glimpse into the past of the shuttered Essex County Hospital Center, where mentally ill patients were treated for 110 years. “Today is Tuesday. Next meal supper.” The date was Feb. 27 — the last day 145 patients were housed at the dilapidated center before they moved to a gleaming, modern hospital down the road. Now, emptiness pervades the old complex, which sprawls over 100 acres of winding roads, towering willows and overgrown grass. Soon the hospital will be gone, most likely replaced by private residences in one of the largest development projects in Essex County in some time, said James Paganelli, executive director of the county improvement authority. Many of the 40 buildings left on the grounds have been vacant for decades. Some have been almost consumed by vegetation. Stacks of mattresses can be seen through the window of one darkened ward; a gurney waits on the porch of another. Signs point to the long-defunct pharmacy that served thousands in the center’s heyday, before new medications developed in the 1950s and ’60s led to mostly outpatient treatment of those with mental illness. The greenhouses where patients grew lilies to sell to generations of townsfolk at Easter are shattered wrecks. The tracks that brought trainloads of coal to the power plant are barely visible. The center is one of 21 hospitals in the state that have closed over the past 15 years, according to the New Jersey Hospital Association. A developer is turning the Art Deco-style Jersey City Medical Center into a luxury high-rise condominium complex. Passaic Beth Israel Hospital was demolished, and three schools are planned for the site. The complex in Cedar Grove is the final piece of a redevelopment project that began 12 years ago, Mr. Paganelli said. So far about 173 acres that housed some hospital property and other Essex County buildings have been sold to the developer K. Hovnanian for $34.4 million. The developer is building 78 luxury single-family homes on land in North Caldwell, Caldwell, Cedar Grove and Verona. It is also building two communities, totaling about 200 units, for residents over 55 years old. K. Hovnanian and Cedar Grove are negotiating what will be built on the parcel where the hospital buildings stand, although a $21.5 million purchase price has been set. That money, and the other land-sale proceeds, will pay down county debt. The buildings, most of which date to the 1890s, will almost certainly be torn down, officials say. “We’re looking for some sort of mix of single-family houses with condos or townhouses along with some senior housing,” said Thomas Tucci, the Cedar Grove township manager. To some, the hospital grounds are literally a ghost town. During a recent tour of the property, Tom Hamilton, an assistant hospital director, said there were tales of a spirit in Building 5. “I went up there once to check it out,” he said. “I got to this point inside the building and all the hair on my arms stood up. I thought, I’m either afraid or there’s an energy here.” Mr. Hamilton has also entered the network of underground tunnels that employees used to travel from building to building. A mile away, the new $58 million hospital has huge windows, a fenced-in yard, a host of programs and a lobby where a programmed piano plays classical music. The library is named for Regina Palo, a volunteer who advocated for 25 years for a new hospital. Her son was hospitalized five times for schizophrenia at the old center; she recalled visiting him in sweltering summers when patients did without air-conditioning and basic supplies. Ms. Palo said she did not particularly care what happens to the old center. “Too many unhappy memories,” she said. But, she said, “We’d like to keep the history of the hospital because I think it’s important for us to know what we should do for the future.”