Detect if point in a polygon based on latitude / longitude

I would like to find only C # on the server side, regardless of whether the latitude / longitude coordinate is within the region (polygon) consisting of points based on latitude / longitude. I believe the correct way to do this is raycasting, but maybe there is already a C # implementation, since this is not trivial?

In addition, I understand that SQL Server has some geometry function, such as STIntersects, but in order to use this, I need to start SQL Server 2008, and each check will be associated with an unwanted database connection.