84 Lumber is an operated American building materials supply company. Founded in 1956 by Joseph Hardy, it derives its name from the unincorporated village of Eighty Four, Pennsylvania, a census-designated place 20 miles (32 km) south of Pittsburgh, where its headquarters are located. In 1992, Joe Hardy's daughter, Maggie Hardy, took over as president of the company. Within her first year as president, the company reached $1 billion in revenue for the first time in history.

As of June 2020, 84 Lumber owns and operates over 250 stores in 30 states throughout the country; the company has more than 5,600 employees and generates in excess of $3.9 billion in annual revenue. Today, it is the largest privately held supplier of building materials to the construction industry.

The company operates components plants, door shops, installation centers and wood products shops. In 2020, it expanded to kitchen and bath design services with the opening of more than 30 design studios within its existing stores.^{[citation needed]} The company's stores carry a variety of materials including siding, decking, windows and trim, roofing and trusses.

Located 20 mi (32 km) south of Pittsburgh, 84 Lumber established its roots in Eighty Four, Pennsylvania, a rural community that has endured as a farmland community. 84 Lumber flourished with the funds and determination of Ed Ryan and Jack Kunkle, Joe Hardy and his two brothers Norman and Bob Hardy. Together, these men collected $84,000 for land and buildings to grow their business. As the business expanded, Hardy and his brothers became sole owners of the company.

84 Lumber established a cash and carry system; customers paid by cash or check, if merchandise was unable to be “carried” out, an additional charge was implemented to have the item personally delivered.

Throughout the 1960s, 84 Lumber continued to expand locations. This was accomplished largely by keeping overhead low and adopting a 'no frills' warehouse-style approach to most of its stores (many of which were unheated, even in cold-climate locations), as most of its clients were commercial customers not overly concerned with aesthetics. By 1981, 84 Lumber had expanded to 339 stores, 283 of which had opened within the previous 10 years, generating revenues of $478 million.

In 1984, the company undertook an expansion plan to open at least 30 new stores. Along with grand openings, stores were remodeled and renovated from no-frills lumber yards to new and improved building materials stores. In 1987, as the improvement plan generated success, the business opened its strict policy of cash-and-carry to options of using credit.

After 34 years of running the company, Joe Hardy appointed his daughter Maggie Hardy president and owner in 1992. Joe Hardy passed 40 percent of the company stock to Maggie that year as well, and added another 40 percent the following year. With a new leader, 84 Lumber continued to expand and reached $1 billion in sales for the first time in 1993 and opened its 400th store in 1997 in Ephrata, Pennsylvania.