Here's an example with contrived data. If it doesn't work on your actual data, it could be due to malformatted entries.
suppressPackageStartupMessages({
library(dplyr)
})
nd <- c("Adams","Barnes","Benson","Billings","Bottineau","Bowman","Burke","Burleigh","Cass","Cavalier","Dickey","Divide","Dunn","Eddy","Emmons","Foster","Golden Valley","Grand Forks","Grant","Griggs","Hettinger","Kidder","LaMoure","Logan","McHenry","McIntosh","McKenzie","McLean","Mercer","Morton","Mountrail","Nelson","Oliver","Pembina","Pierce","Ramsey","Ransom","Renville","Richland","Rolette","Sargent","Sheridan","Sioux","Slope","Stark","Steele","Stutsman","Towner","Traill","Walsh","Ward","Wells","Williams")
counties <- rep(nd,3)
day1 <- rep(as.Date("2020/3/9"),length(nd))
day2 <- rep(as.Date("2020/3/10"),length(nd))
day3 <- rep(as.Date("2020/3/11"),length(nd))
dates <- c(day1,day2,day3)
set.seed(42)
counts <- sample(1:20,length(nd),replace = TRUE)
dat <- data.frame(county = counties, date = dates, count = counts)
dat %>% group_by(county) %>% summarise(cases = sum(count)) %>% print(., n = Inf)
#> # A tibble: 53 × 2
#> county cases
#> <chr> <int>
#> 1 Adams 51
#> 2 Barnes 15
#> 3 Benson 3
#> 4 Billings 30
#> 5 Bottineau 12
#> 6 Bowman 54
#> 7 Burke 51
#> 8 Burleigh 45
#> 9 Cass 21
#> 10 Cavalier 12
#> 11 Dickey 15
#> 12 Divide 42
#> 13 Dunn 60
#> 14 Eddy 54
#> 15 Emmons 45
#> 16 Foster 9
#> 17 Golden Valley 27
#> 18 Grand Forks 12
#> 19 Grant 15
#> 20 Griggs 39
#> 21 Hettinger 15
#> 22 Kidder 60
#> 23 LaMoure 6
#> 24 Logan 24
#> 25 McHenry 9
#> 26 McIntosh 3
#> 27 McKenzie 30
#> 28 McLean 33
#> 29 Mercer 45
#> 30 Morton 24
#> 31 Mountrail 12
#> 32 Nelson 12
#> 33 Oliver 54
#> 34 Pembina 39
#> 35 Pierce 15
#> 36 Ramsey 12
#> 37 Ransom 6
#> 38 Renville 54
#> 39 Richland 9
#> 40 Rolette 51
#> 41 Sargent 54
#> 42 Sheridan 18
#> 43 Sioux 18
#> 44 Slope 6
#> 45 Stark 60
#> 46 Steele 9
#> 47 Stutsman 6
#> 48 Towner 18
#> 49 Traill 30
#> 50 Walsh 24
#> 51 Ward 15
#> 52 Wells 3
#> 53 Williams 51