Which two English counties are linked by the Dartford Crossing?

When I travelled to France from Northampton in the early 2000s I was looking for signage for the Dartford Tunnel . I asked my wife what they meant by Dartford Crossing. When she said the Tunnel had been replaced by a bridge I was very surprised . When I saw the bridge I was absolutely terrified . I absolutely hate heights - even ladders . I did manage it that night and several times since. It still terrifies me . Northbound tunnels are fine .