Vacant land is generally taxed the same basic way as improved property: the county assesses a value for the parcel, and that assessed value is multiplied by the local millage rate to arrive at the tax bill. In that sense, the mechanics aren't fundamentally different from how a home is taxed.
The key difference is exemptions. A homeowner living in their primary residence can often claim an owner occupied exemption that reduces the taxable value of the property. Vacant land has no owner living on it, so that exemption does not apply, meaning the land is generally taxed on a larger share of its assessed value than an equivalent owner occupied home would be.
One factor that can lower the picture on the land side: agricultural use classification, where a parcel qualifies, assesses the land based on its agricultural use value rather than its full market value, which can meaningfully reduce the tax bill compared to land assessed at market rate for other purposes. Eligibility for that classification depends on actual use and often a minimum acreage or income threshold that varies by county.
Because assessed values, millage rates, and agricultural use eligibility all vary by county, the county assessor's office is the right place to get the actual numbers for a specific parcel. A CPA can help fold the expected tax bill into a broader holding cost projection.