Lake County Economic Development web page - "Lake County’s 2018 population was estimated to be more than 342,000, with a growth rate of 3.16% in the past year according to most recent United States census data. Lake County has ranked among the top 10 fastest growing counties in Florida. As the Orlando urban core continues to approach build-out, Lake County is expected to experience significant population growth over the coming decades. Forecasts predict Lake County’s population to grow more than 427,000 by 2030 and more than 484,000 by 2040."
Source: BEBR Bureau of Economic and Business Research, University of Florida Florida Estimates of Population 2018