Absolutely not! This is so hard to understand but most tax assessors do not actually come out and evaluate your property, not to mention taking into account improvements, condition, upgrades etc. And they generally are not doing a drive by either. They use a statistical formula based on market trends etc to formulate a value. Most assessors don't actually enter a property but maybe every 10+ years, there are just too many.
The best place to find out market value of a home is with a CMA (comparable market analysis) performed by a Realtor. An agent can pull the most recent sales data and actually compare the homes side by side in terms of baths, bedrooms, square footage, upgrades, renovations, updates. As an agent, I will sometimes look at the tax assessment values vs sold prices of recent homes to get an idea of what percentage range they are in comparatively, but honestly I don't put much weight on the value itself. Solely what the relationship has been between the 2 values.
Get a great agent with lots of knowledge about the area you are pursuing to make sure you are getting the right deal. No county assessor could tell you that!