updated 2/12/2020
Below is statistical data from the Texas Health and Human Services website for Travis, Tarrant, Dallas, Denton and McLennan counties. These counties were chosen for a number of reasons.
Dallas county sprays pesticides for mosquitoes more than the other counties and has at times resorted to aerial spraying while the City of Austin, which is basically Travis county, has not sprayed for mosquitoes in 14 years and McLennan county, which is basically Waco, has not sprayed since the 1980s. Denton county, which borders Tarrant county to the north, has a much higher trigger threshold before they resort to spraying and is in the same geographical region as Dallas and Tarrant counties.
Spray proponents will tell you that you cannot compare counties WNV infection rates as there are many variables but it is very interesting to note that the City of Austin and McLennan county, that do not spray for mosquitoes, and Denton county, that sprays considerable less than Tarrant and Dallas counties have a lower overall infection rate than a county that has resorted to aerial spraying.