This paper presents a methodology for estimating the size and composition of the Ontario labour force eligible for coverage under the Ontario Workplace Safety & Insurance Act (WSIA). Using customized tabulations from Statistics Canada's Labour Force Survey (LFS), we made adjustments for self-employment, unemployment, part-time employment and employment in specific industrial sectors excluded from insurance coverage under the WSIA. Each adjustment to the LFS reduced the estimates of the insured labour force relative to the total Ontario labour force. These estimates were then developed for major occupational and industrial groups stratified by gender. Additional estimates created to test assumptions used in the methodology produced similar results. The methods described in this paper advance those previously used to estimate the insured labour force, providing researchers with a useful tool to describe trends in the rate of injury across differing occupational, industrial and gender groups in Ontario.