Rockville, Md. ? In the brisk Washington real estate market, the white colonial was an easy sale – three bedrooms, easy access to a major commuting route and an acre of land, a rarity in the tightly packed suburbs.

However, the 18th-century house had one thing the McMansions could never claim – the original Uncle Tom’s cabin.

Attached to the side is a small, one-room building, its walls made of graying split oak beams.

A massive stone chimney rises at the back, above the large hearth where slaves once tended meals for a plantation owner.

Among the farm’s slaves was Josiah Henson, the man whom Harriet Beecher Stowe used as a model for the Uncle Tom character in her 1852 novel on slavery, “Uncle Tom’s Cabin.”

Less than a month after being put on the market for about $1 million, the cabin and the house are being purchased by Montgomery County.

“We don’t want it to turn into a dentist’s office,” said Peggy Erickson, executive director of Heritage Montgomery, an agency that promotes historic tourism and that worked with the county to raise money to buy the house.

The owners signed a contract last week with the county, rejecting rival bids from a group of doctors who wanted to establish a center to study world health and from a private bidder. The sale price wasn’t immediately released. The sale is expected to be final at the end of January.

Greg Mallet-Prevost’s parents had owned the house since the early 1960s, and he put it up for sale after his mother died in September at age 100. The Mallet-Prevosts were history buffs and took great care of the cabin, he said.

The house was once the anchor of a 3,700-acre farm that sprawled over much of modern-day Rockville.

It was owned by Isaac Riley, who bought Josiah Henson and his mother in the 1790s.

Henson was born in 1789 and sold to Riley roughly five years later.

In his 1849 autobiography, Henson recalls how his mother pleaded with Riley to purchase both her and her child, and was beaten by Riley as she clutched his legs.

“This was one of my earliest observations of men; an experience which has been common to me with thousands of race, the bitterness of which its frequency cannot diminish to any individual who suffers it,” Henson wrote.

He recounted beatings and grueling work for Riley, but also some pride that Riley eventually appointed him manager of the farm. Of his quarters, Henson wrote of “the cabin used for a kitchen, with its earth floor, its filth, and its numerous occupants.”

When Riley fell into debt, he had Henson lead a group of slaves to his brother’s Kentucky farm to protect them from creditors. The group passed through Ohio, then a free state, but Henson decided against running away to keep his word to Riley. When Riley later reneged on a promise to free him, Henson and his family escaped to Canada in 1830 through the Underground Railroad.

Stowe cited Henson and his choice not to flee in Ohio as one of her sources for Uncle Tom, the dutiful and suffering slave who obeys his master’s wishes against his own best interest.

Stowe’s book was a catalyst for abolitionists in the pre-Civil War slavery debate.

The Uncle Tom character was eventually seen as a traitor to his race, and the name became an insult for black people who act subservient to white people.

That characterization overlooks Henson’s later life in Canada, where he founded a settlement at Dresden, Ontario, that welcomed escaped slaves, said Steven Cook, manager of the Uncle Tom’s Cabin Historic Site there.

Mallet-Prevost said he and his two siblings sold in part because they couldn’t afford to maintain it.

“The best thing for this house is to have the county own it and keep it open to the public,” he said.