We have been mowing the land adjacent to ours for 20+ years. We do know who the owne is, but as it is a little more than an acre and is at the edge of our property we have taken care of it. The owner recently died and her son had the land surveyed. We attempted to find out what their plans were for it, but no one has called us back. Can we attempt to take over this land under squatters rights? No one has visited that land since we've been attending to it.

Its called Adverse possession, not squatters rights. But I doubt if just mowing the property would be enough. You would have to have used the property without the owner's permission for a proscribed period.

This site gives a good explanation of Adverse Possession and the PA requirements:
Adverse Possession laws - Information on the law about Adverse Possession - Requirements - Yrs, Disability, Title, Lifted, Color, and Taxes (http://law.jrank.org/pages/11865/Adverse-Possession.html)

Adverse [possession is one name and open and notorious possession is also another name. Your mowing of the property does not meet the requirements of adverse possession which can vary from state to state. Have you paid the taxes on this property? Has the owner?