According to this piece by Andrew McGill of CityLab/The Atlantic, the average American yard has shrunk by 26 percent since the 1970s, as homes get larger while lots get smaller:

The shrinking lawn is actually an economic compromise. Americans want bigger houses, but since every additional square foot balloons the cost, homebuilders are keeping prices affordable by cutting off lawn acreage.

The happy side effect is a reduction in new homes’ consumptive use of water.