We examine the extent and correlates of part-year manufacturing during the late nineteenth century using unpublished data from the manuscripts of the 1870 and 1880 censuses of manufactures. These are the earliest comprehensive estimates available on this topic. Although the typical manufacturing plant operated full-time, part-year operation was not uncommon. Indeed, the likelihood of part-year operation varied across industries and location and with plant characteristics, and workers in such plants received higher monthly wages than those in firms that operated year-round, compensating them for the loss of work and possible inconvenience.