Objectives To determine the trends in incidence, prevalence and mortality of systemic lupus erythematosus (SLE) in a US population over four decades. Methods We identified all the patients with SLE in Olmsted County, Minnesota who fulfilled the European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR) criteria for SLE during 1976-2018. Age-specific and sex-specific incidence and prevalence rates were adjusted to the standard 2000 projected US population. The EULAR/ACR score was used as a proxy for disease severity. Standardised mortality ratio (SMR) was estimated. Results There were 188 incident SLE cases in 1976-2018 (mean age 46.3±SD 16.9; 83% women). Overall age-adjusted and sex-adjusted annual SLE incidence per 100 000 population was 4.77 (95% CI 4.09 to 5.46). Incidence was higher in women (7.58) than men (1.89). The incidence rate increased from 3.32 during 1976-1988 to 6.44 during 2009-2018. Incidence rates were higher among the racial and ethnic minority populations than non-Hispanic whites. The EULAR/ACR score did not change significantly over time. Overall prevalence increased from 30.6 in 1985 to 97.4 in 2015. During the study period, there was no improvement in SMR over time (p=0.31). Conclusions The incidence and prevalence of SLE are increasing in this US population. The increase in incidence may be at least partially explained by the rising ethnic/racial diversity of the population. There was no evidence that the severity of SLE has changed over time. The survival gap between SLE and the general population remains unchanged. As the US population grows more diverse, we might continue to see an increase in the incidence of SLE.