Grandfather Clause...

My family has owned the property beside my parents house since 1974.  It was purchased for the purpose of maintaining a mobile home, first for my grandmother, then my siblings and our children getting their start.  My large family has lived in this community since the early 1940's, possibly before.  A few years ago the community decided to 'incorporate'.  Last Labor Day the mobile home burned due to an overloaded extension cord.  Now the community's Mayor is saying the community has been rezoned and we won't be able to replace the mobile home.  My sister is homeless, lives on SSI and can't afford to build.  There has been very few new homes built in the community since I was a child 40 years ago.  I don't like new rules being made up for people that have always lived here.  The ONLY reason the community decided to incorporate was to have better water and sewage.  It was always a peaceful and quiet community without police.  Now police are constantly being called to an area now known for drugs.  Shouldn't we be grandfathered in?  From what I've been able to gather on the internet, the property and it's owners are grandfathered in and changes can only be made if it were sold to someone else.  Is this true?  I've already bought the replacement mobile home, but have run into a snag with the man contracted to clean up the property and now have to take him to court.  The mobile home has to be moved by July 1st.  Please, does anyone have any knowledge they can help me with?