ITHACA, N.Y. — The 2018 census estimates released last week held a number of surprises for communities across the state and nation, and Tompkins County was no exception.

The latest estimate suggests the county has barely grown and might have even dipped in population in some recent years. As a local expert points out, the estimate may be lower this year due to a methodological change. However, there could still be ramifications, particularly in the realm of funding, for a county that despite all of its development, does not appear to be growing much in population.

Putting the 2017 and 2018 census estimates side by side, there is a difference of about 2,000 people. To say this is an unusual amount of change would be an understatement. The revisions from the 2016 to 2017 estimates amounted to a difference of a couple hundred people. A change of over 2,000, almost 2% of the county’s population, is a little harder to explain away.

The first question that comes to mind is, why don’t the numbers show more growth? The area’s recent construction uptick is well-documented. From 2010 to 2017 (the most recent complete year available), 2,418 homes and apartments were built in Tompkins County, resulting in a net increase in housing supply of 5.6%. From 2010 to 2018, the county added about 6,000 jobs. The economic growth is there, the housing growth is there, but those do not necessarily add up to population growth. More jobs might just mean more people commuting in from outside the county, for example.

There has been modest growth in the local student population, based on enrollment data from Cornell University and Ithaca College. Presumably, Cornell and Ithaca College keep closer tabs on its student population than the census does on its estimates, and unlike Tompkins-Cortland Community College, they’re more likely to draw populations from outside the area. In 2010, there were 20,939 students on Cornell’s Ithaca campus, and in 2018, there were 22,188 students on the Ithaca campus, a gain of 1,249 students. Meanwhile, Ithaca College saw an enrollment drop of 432 students over the same eight-year period, from 6,949 to 6,517.

In any case, none of this explains why the Census Bureau revised its Tompkins County 2017 estimate by more than 2,000 people.

For an explanation on that, we turn to more knowledgeable sources. Jan Vink is an Extension Associate with Cornell’s Program on Applied Demographics, which compiles and analyzes demographic and economic statistics and trends. According to Vink, the large change wasn’t the result of anything that the Census Bureau explicitly saw, but rather the way something was calculated — that something being international migration into states and counties, those born in other countries who now live in Tompkins County (and vice-versa, those who move out of the county to other countries).

“It had a big impact on New York State. They use data from ACS (the American Community Survey, which is compiled using a sampling of the population) to create those estimates. First at the top (the national level), then the state, then the county. They divide the migration into the U.S. over the states and over counties,” explained Vink.

“Total inflow hasn’t changed. What has changed is the way they distribute over the states. ACS asks if someone was foreign-born and where they lived last year. Both can be used to distribute. Previously, they only used the year of entry (i.e. if they were foreign-born), and looked at how many lived in New York to distribute. This time, they used the other question, where people lived last year. I am not sure why the change in methodology makes such a difference in New York. The year of entry is still used to apportion out at the county level.”

Vink also cited another reason for Tompkins County’s lethargic growth and the population declines of its neighbors — the graying population.

“Migration gets a lot of attention, but differences in the birth and death rates are getting smaller as the population ages,” Vink said.

As for the construction activity and new housing? “One thing to consider is household size, the number of people living in the same housing unit has been decreasing. As households get smaller, you can have slow or no population growth and still have a need for new housing units. This is especially true with aging households,” replied Vink.

With the revisions to the way the estimates were calculated, Tompkins now looks like it added much fewer people during the decade than previously, and well below both natural population growth and the average growth in the United States (5.96%). Whether the latest estimate is accurate is questionable, but it still has ramifications – policy decisions such as where to disburse affordable housing funds, because if an area isn’t really growing, then it looks less like to need those funds. As a Census document describing the 2018 estimate methodology points out, these yearly population estimates are “used for federal funding allocations, as controls for major surveys … for community development, to aid business planning and as denominators for statistical rates.”

Vink urged caution when making conclusions from the estimates.

“There’s a risk when magnifying details that emphasis is placed on things that shouldn’t be. One of the first things I would do is put it on a chart and focus on the overall trend. One or two percent is minimal change.”

It’s a mixed bag with the census estimates. Sometimes they’re pretty good: the census estimate for Tompkins County was only off by 30 people when the 2010 Census was tallied up. But in other cases, it’s really bad. The initial Census Bureau estimate turned out to be over 12,000 people short for Onondaga County (Syracuse area) when the 2010 census was conducted. We won’t have truly accurate numbers for Tompkins County until March 2021.

Brian Crandall reports on housing and development for the Ithaca Voice. He can be reached at