Resolving this error: "cannot transform sfc object with missing crs"

Question

I am attempting to outline a specific grouping of census tracts over entire US states.

This is the code I am attempting to run:

sf_states <- sf::st_as_sf(fifty_states, coords = c("long", "lat")) %>%
  group_by(id, piece) %>%
  summarize(do_union = FALSE) %>%
  st_cast("POLYGON") %>%
  ungroup()

illinois <- sf_states %>%
  filter(id == "illinois")

arlington.crs <- arlington.test %>%
  st_set_crs(4326)

ggplot() +
  theme_minimal() +
  geom_sf(data = illinois) +
  geom_sf(data = arlington.crs, col = "green", alpha = 0, size = 2)

The arlington.test data is coming from the tidycensus package and includes the associated geometry for each census tract.

However, when I run the code, I get the following error:

Error in st_transform.sfc(st_geometry(x), crs, ...) : 
  cannot transform sfc object with missing crs

I tried dozens of different answers I have come across on StackOverflow and nothing seems to make this work.

What makes it even more strange is that I can run the two geom_sf functions with ggplot separately, and they plot just fine.

The error only occurs when I attempt to run them together, as shown in the included ggplot code above.

Any other thoughts/ideas?

Thanks in advance.

Edit (to answer the question below):

> sf::st_crs(arlington.test)
Coordinate Reference System:
  User input: NAD83 
  wkt:
GEOGCRS["NAD83",
    DATUM["North American Datum 1983",
        ELLIPSOID["GRS 1980",6378137,298.257222101,
            LENGTHUNIT["metre",1]]],
    PRIMEM["Greenwich",0,
        ANGLEUNIT["degree",0.0174532925199433]],
    CS[ellipsoidal,2],
        AXIS["latitude",north,
            ORDER[1],
            ANGLEUNIT["degree",0.0174532925199433]],
        AXIS["longitude",east,
            ORDER[2],
            ANGLEUNIT["degree",0.0174532925199433]],
    ID["EPSG",4269]]
> 

Answer 1

Your arlington.test object seems to be in EPSG:4269; you attempted to override it to WGS 84 via sf::st_set_crs(4326). Are you certain you did not mean sf::st_transform(4326)?

The set crs is best reserved for cases you are certain the CRS is malformed / incorrect (it can happen when the *.prj gets lost from your *.shp shapefile). This is not a typical use case for {tidycensus} data.

To change projection from one known CRS to another sf::st_transform() works the best.