A few key points are legible in this graph. The first is that the time when moms made up the biggest part of the country’s demographics was from around 1975 to around 1995. (This is true for as far back as quality data is available—and possibly back to the nation’s founding, but mostly because of shorter life spans in earlier times, not lower fertility.) Since then, the share of the population composed of moms has eroded considerably. A holiday that once celebrated as much as 28 percent of the American population now celebrates less and less each year; a drop of a percentage point may not seem like much, but as a share of the country, it represents millions of people.
And there’s a natural follow-on trend to notice: As the dark gray line in the above graph shows, moms living with their own kids represent a shrinking share of the population too. This makes intuitive sense: Minors are much more likely to live with their parents than are the group of people with living mothers generally, and so if the fertility rate falls, so would the percentage of the population who are moms with kids in the house.