Despite the damages that he sustained during the Civil War, James Gambrill's milling business continued to thrive in the postwar years. As perhaps the most conspicuous symbol of his success, his Second-Empire style house ("Edgewood") was constructed sometime around 1872, commanding an expansive view of his mill and farm. Although in most architectural respects Edgewood was typical of pattern book designs from the period,  with its distinctive mansard roof and central tower, the three-story brick home was nevertheless one of the very few full-scale Second Empire structures ever built in Frederick County.

The main block of the house was richly ornamented and constructed on a double-pile center-passage plan. A broad porch spanned the length of the northwest front facade, and upper-story balconies projected from the second and third floors. A long three-story service wing was integrated into the rear of the house, forming an ell. Gambrill later added an enclosed rear porch, divided into a lower level summer dining room and an upper level solarium.

The house was elaborately furnished and designed with spacious and elegantly detailed rooms. It was suited to both the functional domestic requirements of the Gambrills' large family and their fondness for entertaining guests in grand style on special social occasions. A double parlor, a library, and a dining room were on the first floor, while large-scale entertaining was accommodated by the third floor ballroom and built-in stage. Seven fireplaces were built in the house, with imported Italian marble used for the mantels and hearths of those on the first floor. A continuous balustrade complemented the central walnut staircase extending in an open stairwell from the first to third floors.

The architectural sophistication of the mansion was supported by mechanical features considered highly progressive at the time. These included a coal-burning furnace, gas wall-mounted lamps throughout the house, a gas cooking range, and an innovative plumbing system providing hot and cold running water and sewage disposal. A large cistern remains behind the mansion where water, pumped from a spring several hundred yards to the north, was stored and delivered to the house by gravity for domestic use.

A contemporary newspaper account recounted a gala summer concert at the Gambrill's graceful country estate:

AT BEAUTIFUL EDGEWOOD

Another Evening with the Estey Philharmonic Orchestra

The large picnic wagon of Mr. H.C. Zacharias and its four prancing steeds were again called into requisition last night to convey the members of the Estey Philharmonic Orchestra to Edgewood, the delightful country home of Mr. and Mrs. James H. Gambrill, beautifully located on a hill directly overlooking the many-curved Monocacy, its well-arranged lawn sweeping toward the shore of that romantic stream. ... As the team drew up at the door of the beautiful home at Edgewood the cheers of the ladies assembled on the verandah greeted the musicians. ... The house was brightly illuminated, its wide doors were thrown hospitably open, and across the velvet green carpet of the lawn the beams of the moon were mellowly cast. Amid the trees hung Chinese lanterns, and here and there, in the summer houses and elsewhere, were refreshment tables and groups of chairs where the guests might gather to hear the music. The orchestra were conveniently positioned on the northwest wing of the front verandah. ...

In 1897, however, during a period of national recession, Gambrill was forced to surrender title to his estate and mills. Gambrill's finances had been strained by the costs of rebuilding his mill in Frederick after it was destroyed by fire in 1893 and by fierce competition from more technologically advanced milling operations in the Upper Midwest.  The properties were conveyed to his daughter and son-in-law, and shortly thereafter sold out of the family. Gambrill retired to Frederick, where he lived until his death in 1932 at the age of 102. Araby Mill was never reactivated after his ownership.

The National Park Service acquired the Gambrill House in the 1980s. It currently serves as the headquarters for the Historic Preservation Training Center (HPTC), an organization dedicated to training maintenance workers in historic preservation skills and preserving historic structures throughout the National Park Service system.