The Preserver 16:1 (August 2008) asks, “What happened to the 1890 Census?” 47,000 enumerators collected information on 62 million Americans. On the afternoon of January 10, 1921, smoke was seen wafting from the Commerce Building in Washington, D.C., where the 1890 schedules were stored. The fire was confined to the basement, but the basement was flooded in the effort to put out the fire.
Some census schedules stored on the fifth floor of the Commerce Building were not damaged. Other schedules stored in a supposedly waterproof vault in the basement received minor damage. The 1890 schedules, while in the basement, were not in the vault. They were thoroughly soaked. To add insult to injury, the decision was made to allow the soggy schedules to remain in the flooded basement until a damage assessment could be done the next day!
A small part of the 1890 schedules in fact survived, but these fragments only cover very small sections of ten states and the District of Columbia. The cause of the fire was never ascertained- officially it was suggested that some papers had spontaneously combusted, but a second, more widely-believed theory held that a worker smoking in the basement set off the blaze accidentally.
NARA 1890 Census Fact Sheet: http://www.archives.gov/genealogy/census/1890/1890.html