Penumbra Plantation was an antebellum plantation estate in St. Charles Parish, Louisiana. It was built in 1821 by the Pendergast family and is on the National Registry of Historic Places.

The 65-acre estate featured a long white gravel lane lined by Spanish moss hung from black oaks, leading to a circular drive in front of a stately two-story Greek Revival-style plantation house. To the right of the house lay a hedged arboretum; a weeping hemlock within marked the entrance to the Pendergast family plot, where many of the remains from the crypt beneath the Maison de la Rochenoire had been reinterred after the fire. Beyond the house were a cypress grove and extensive gardens, and a white-painted stable behind had been converted to a garage with several bays. The house and grounds were maintained by a Pendergast family manservant known only as Maurice.

Penumbra Plantation was owned by the Pendergasts from the time of its construction. After Rochenoire was burned to the ground, Penumbra became the primary residence for the family's Louisiana branch. Aloysius and Diogenes Pendergast spent quite a bit of time there as children, and Aloysius and his wife Helen would later take up residence there after they were married in the estate's formal garden.

At the conclusion of the events of Blue Labyrinth, despite his earlier statement that "the Pendergasts never sell real estate," Pendergast divested himself of all of the family's holdings purchased with profits of Hezekiah Pendergast's infamous elixir—including Penumbra, which Southern Realty Ventures planned to turn into a development of sixty-five single-acre custom mansionettes called Cypress Wind Estates. The old mansion would serve as the clubhouse; Pendergast had arranged for Maurice to be given a job as its wine steward until his retirement.
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