The average effective property tax rate in the county is 1.34%, the sixth highest rate in Maine. Knox County With a population of almost 40,000, Knox County is one of the smaller counties in Maine. Are you looking to move to a town or city in Maine, but also want to get a sense of what the property tax (or mil rate) is?You’ve come to the right place. I created this page after constantly Googling the rates. The state of Maine publishes this information in a PDF, but wanted to be able to sort by mil rate, county, growth rate, and current mil rate. The median property tax in Maine is $1,936.00 per year for a home worth the median value of $177,500.00. Counties in Maine collect an average of 1.09% of a property's assesed fair market value as property tax per year.. Maine is ranked number twenty out of the fifty states, in order of the average amount of property taxes collected.