This is a list of glass factories that operated in Blackford County, Indiana, United States. Natural gas (and later crude oil) was discovered in Blackford County in 1887. This discovery marked the start of Blackford County's participation in the Indiana Gas Boom. Manufacturers, especially glass makers, were lured to the area with promises of free gas, free land, and (in some cases) cash subsidies. Hartford City Glass Company, Sneath Glass Company, and Johnston Glass Company were the largest glass companies during the gas boom. The current Hartford Glass Company is the longest lived. During the 1890s, the Hartford City Glass Company was the third-largest window glass producer in the United States, and Sneath Glass Company was the country's largest producer of lantern globes.