Lawrence’s population mystery soon may be over.

City officials are ready to acknowledge the city’s population didn’t grow as much over the past decade as they once thought — but they still believe the U.S. Census Bureau has undercounted the city’s population by about 2,400 people.

City commissioners at their Tuesday evening meeting will be asked to send an official letter asking the Census Bureau to review evidence gathered by city staff that suggests there were about 90,000 people living in the city in 2010 rather than the official Census count of 87,643.

The appeal could end a multi-year disagreement between the city and the Census on population totals.

“At the end of this process, I think we’re going to be much closer to knowing how many people actually are living in Lawrence,” said Amy Miller, a planner who has been leading the Lawrence-Douglas County Planning Department’s review of the Census numbers.

This much already seems certain: There aren’t as many people living in Lawrence as leaders once thought. In 2010, the city’s planning department estimated there were 92,727 people living in the city.

If a number near 90,000 ends up being the new 2010 Census population figure, the city will be about four years behind where it thought it was. The city estimated it cracked the 90,000 barrier in 2006.

Miller said it is important for the city to have an accurate population number because planners rely heavily on the figure for tasks such as transportation planning or planning for new water and sewer infrastructure, which is heavily dependent upon population growth.

In addition, population figures are used to calculate some federal aid and grant programs available to the city.

Miller said he believes the city has a good chance of having its population total adjusted upward. Since late 2011, city staff members have been reviewing building permits, utility bills and data from the Douglas County Appraiser’s office to determine how many housing units exist in specific areas of town.

Staff members honed in on 10 Census tracts where it appeared the Census Bureau had undercounted the number of living units by at least 10 units.

In total, the city is contending the Census Bureau undercounted the number of living units in the city by 593. Miller said the undercounted areas were spread across the city, but she thinks student housing areas may have been more impacted.

“I can’t say for sure, but I think a lot of the discrepancies will be single-family homes that have been converted to multifamily use,” Miller said.

Miller said the city has good documentation about the number of housing units that have been added to the city since 2000, when the previous Census was taken.

As for why the city’s internally produced population estimates appear to have been high, Miller now suspects that the city’s 2000 Census count may have been inflated.

In other words, Lawrence may not have grown as much during the 1990s as the Census Bureau indicated. The city used the 2000 Census population total as a baseline to create population estimates for the following years. If the 2000 Census count was inflated, all of the city’s subsequent population estimates would have been inflated too.

Regardless, even if the Census Bureau revises upward the city’s 2010 population totals, the decade of the 2000s will still go down as one of the slower growth periods for the city.

If the city’s new 2010 population number is at about 90,000 people, the city will have posted population growth of 12.3 percent from 2000 to 2010. In both the 1980s and 1990s, the city’s growth rates were closer to 20 percent.