Is there an inheritance tax when land is sold (in Massachusetts) that was acquired over 18 years ago.

No - if inheritance tax had been owed it would have had to be paid 18 years ago on the value of the land when it was inherited. Also, MA does not have an inheritance tax.

However, although you didn't ask - if the property is sold at a gain (i.e. if your proceeds exceed your cost basis, which is equal to ther fair market value of the land when it was inherited 18 years ago) then you have a capital gain to report on both your MA and federal income tax returns.