library(tigris)
library(leaflet)
library(tidyverse)

Gather shape file data on Ohio counties, from TIGRIS

oh_c <- counties("Ohio", cb = TRUE)

oh_c <- sf::st_as_sf(oh_c)

Using geom_sf

oh_c <- oh_c %>%
    mutate(del = factor(ifelse(NAME == "Delaware", 1, 0)))

ggplot() +
    geom_sf(data = oh_c, aes(fill = del)) +
    scale_fill_viridis_d() +
    guides(fill = FALSE) +
    labs(title = "Where is Delaware County, Ohio?")

Using leaflet

m <- leaflet(oh_c) %>%
  addTiles() %>%  # Add default OpenStreetMap map tiles
  addPolygons(fill = (oh_c$del == 1),
              fillColor = "yellow", 
              fillOpacity = 0.6,
              weight = 1)
m  # Print the map