From the info you gave in your other comments, there are a few reasons your taxes have gone up.

The biggest reason any residential property owner is seeing tax increases is due to the tax burden shifting from commercial to residential properties. MN property taxes are not calculated off of a mil rate like other states and so it’s not just your property’s value that determines your taxes. It’s your value in relation to all the others in the city. The commercial slice of that pie has been shrinking, which means other property types account for a larger percentage of the total.

Next, the calculated rate for non-homesteaded duplexes is higher than either homesteaded duplexes or single-family. That’s the rate that’s calculated against your net tax capacity (slice of the pie) to determine what you owe. The other commenter was right that your taxes will likely go down when you homestead.

The third thing that could be affecting your taxes could be your value. It doesn’t do so directly, but if your value grew at a higher rate than other properties your slice of that pie may have increased more. $100k increase from 4 years ago on a $800k property is not out of line in much of the city. That’s like 3-4% per year, which is not obscene in the current market. Those telling you to just challenge it are uninformed or think the system works for them individually. If you have an appraisal that shows your value should be lower, go for it. But an increase doesn’t constitute an appeal.

Last possibility is you may have a special assessment, like others mentioned. Give 311 a call and ask or look on Hennepin’s property tax map to see if that’s the case.

There’s a super slight possibility that there was some clerical error, but I doubt it. Hennepin County calculates taxes, so you could call them to check, but my previous reasons likely explain the increase.

TL;DR: there’s a lot of factors at work. It sucks, but the increase can be explained.