Okay, first and foremost allow me to attempt to bring some understanding to the situation as to the reasons local township or county assessors would be visiting your property for assessment purposes. I used to work for the county assessor in the county I grew up in until last September. I know work for a private contractor who works with local county/township government (assessor's offices) providing them valuation services in their appeal processes (when disagreement over what is fair market value of a property is filed by a taxpayer or tax rep on their behalf). With both my past employment and my current I am familiar with assessing offices and the things they have to do in order to hopefully capture proper valuations on properties.
I will stress I work with quite possibly two of the most well ran and professional acting offices, which strive and many times go above and beyond what they have to do in service to their local tax payers and land owners. However, I know first hand not all offices have knowledgeable or fully capable people and practices/actions show this lack of ability.
As for why a local assessing employee would be visiting your property:
-Permit taken out for new structure or sufficient updates requiring a data change that would justify an increase or decrease in assessed value (demo). Many areas the building departments work hand in hand with the Assessors to make the process as efficient and uniform across the tax base as much as possible. In an effort to make no assumptions to sizes, quality of construction or other things many offices will do a field visit instead of "if their office has it" using GIS imagery for measurements.
-New sale of the property. A new sale requires the office to verify the data on the Property Record Card to make sure nothing has changed either in a positive value influence or a negative. This is needed because of the vast amount of changes or updates or demos which can go unlogged with a permit or unreported to the assessing office.
-Request by taxpayer...pretty self explanatory.
-Reassessment. This is the most common one especially with the General Assembly passing that now counties/townships in our state must do a cyclical reassessment (re-analysis) of ALL parcels in a 4 year period in their jurisdiction (25% one year, 25% another year and so on). This is to ensure discrepencies can be caught and the data is as accurate as possible. In order to properly assess a property whether an assessor or an appraisor you must have accurate data. The default cost approach the states use which is than trended relies on this data even more so. This is most likely the case the OP is dealing with....while many counties (I know Elkhart does) send out notices of visits upcoming to the most recent mailing address on record with the county, they technically don't have to atleast I don't think so, but it is encouraged. If the land is posted/gated or blocked off by any means they cannot go around this to my understanding, nor can the require entry into any structure...that will greatly limit the amount of drawn assumptions but it cannot be forced. As for notifying taxpayers some assessors do the mailers like I've stated, but nearly all run a notice in the local papers notifying taxpayers of the visits.
Trust me, most of these field people are just common everyday people (AND YES THEY PAY THE SAME TAXES) just attempting to do their jobs as instructed and then go home each day. Your daughters handled it exactly as they should have, and I know others and myself when I did field work didn't like it when children would answer the door...made me feel uneasy for their sake and would just tell them to close the door and get their parents if their home.
If you own a home or a business and dislike your assessment you have the right to file an appeal within the proper time frames, IT IS YOUR RIGHT! My business can even assist you in this and even represent you if needed, but we cannot take contracts currently in Elkhart or Porter county as we currently assist both in chasing fair market value to their taxpayers that file appeals.
I saw the caps mentioned...and the assumptions assessors are just hiking assessments to make up for them. This SHOULDN'T BE HAPPENING if it is. Indiana is a market value state which means if your assessment can be proven with market evidence to be overstated it is justified that a reduction be sought and done by the county (happens a lot). Just know if you do appeal your assessment it does open the window for the assessment to increase...while many of the assessors I've worked with refuse to "punish" taxpayers in atleast the year under appeal MANY do if it is justified.
Do your most well ran and professional acting offices make appointments with private property owners prior to stepping foot on their private property? Is that their policy?