The longhouse was made of elm bark over a framework of poles. (Birch does not grow far enough south to be widely used by the Mohawks: elm worked just as well). There was a door at each end. Inside, a 10-12 foot wide hallway ran the whole length of the house. Fireplaces lined the middle of the hallway, about every 20 feet. On each side, there was a "shelf" which was about 2 feet off the ground. This was high enough to sit comfortably and allowed people to sleep off the cold ground. The shelves would be about 10 feet wide. An upper shelf, 6 feet above this sleeping platform, was used for storage or as a place for the children to sleep. Under the lower shelf was additional storage.

A family had a section of these shelves to themselves. They shared the fireplace in the middle of the hall with the family on the opposite side. Anywhere from 30 to 100 people might live in a longhouse. All of them were related through the mothers. When a man married, he went to live with his wife's family. The women of the longhouse were, thus, either sisters or else cousins, through a female ancestor.

The Iroquois seem to have considered the longhouse an important social institution and a cozy group home. Whites who lived in them said they were smokey, noisy, utterly lacking in privacy and that children and dogs scampered about at all hours.

The organization of the community into longhouses based on matrilineal descent is reflected in Iroquoian kinship terminology. A child addressed his mother's sisters (who lived in the same longhouse) as "mother" but father's sisters (who lived in another longhouse) were "aunt". First cousins through the female line (who lived in the same longhouse) were "brother" and "sister" while those through a male ancestor were "cousin."

Apparently, when the longhouse got "big", there was a tendency for it to separate, with a portion of the population moving to another site, perhaps only a few feet away, and building their own longhouse. The cause seems to have been that, when the population got too large, the internal bickering mounted. In a large longhouse that had existed for several generations, some of the women might be only 3rd or 4th cousins, without close ties. Thus, one of the older women might. for example, take her several adult daughters and their families and move next door, starting a new longhouse. This would reduce the overcrowding and tensions in the longhouse they left and, since the people who remained in the old longhouse were now usually more closely related, it would actually increase the stability of the group left behind.